Add short execution threshold for ExecutionTime plugin

[Tautvis]

As per issue 1335, I created code change that will hide short execution times.

[jcb91]

Looks good, but the scope of the variable exec_time is a bit gnarly like this

[Etjean]

Hi, I think this feature is good, and it would be great if it could be integrated.

The Appveyor build seems to be failing for the python 2.7 environment. Here is the command and its output that seems to make the build process fail :

%PYTHON_HOME%\Scripts\tox -e %TOXENV%
GLOB sdist-make: C:\projects\ipython-notebook-extensions-ynb9f\setup.py
py27-notebook create: C:\projects\ipython-notebook-extensions-ynb9f\.tox\py27-notebook
py27-notebook installdeps: coverage>=4.2, jupyter_highlight_selected_word>=0.0.5, jupyter_latex_envs>=1.3.4, mock, nose, notebook
ERROR: invocation failed (exit code 1), logfile: C:\projects\ipython-notebook-extensions-ynb9f\.tox\py27-notebook\log\py27-notebook-1.log
================================== log start ==================================
Collecting coverage>=4.2
  Cache entry deserialization failed, entry ignored
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/73/34/c6d83338ccd4cf3f2c47cd71fa63f06e34bd4d4fedfb3b69ee1019bfe25a/coverage-4.5.3-cp27-cp27m-win32.whl (180kB)
Collecting jupyter-highlight-selected-word>=0.0.5
  Cache entry deserialization failed, entry ignored
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/50/d7/19ab7cfd60bf268d2abbacc52d4295a40f52d74dfc0d938e4761ee5e598b/jupyter_highlight_selected_word-0.2.0-py2.py3-none-any.whl
Collecting jupyter-latex-envs>=1.3.4
  Cache entry deserialization failed, entry ignored
Collecting mock
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/05/d2/f94e68be6b17f46d2c353564da56e6fb89ef09faeeff3313a046cb810ca9/mock-3.0.5-py2.py3-none-any.whl
Collecting nose
  Cache entry deserialization failed, entry ignored
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/99/4f/13fb671119e65c4dce97c60e67d3fd9e6f7f809f2b307e2611f4701205cb/nose-1.3.7-py2-none-any.whl (154kB)
Collecting notebook
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/f6/36/89ebfffc9dd8c8dbd81c1ffb53e3d4233ee666414c143959477cb07cc5f5/notebook-5.7.8-py2.py3-none-any.whl (9.0MB)
Collecting traitlets>=4.1 (from jupyter-latex-envs>=1.3.4)
  Cache entry deserialization failed, entry ignored
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/93/d6/abcb22de61d78e2fc3959c964628a5771e47e7cc60d53e9342e21ed6cc9a/traitlets-4.3.2-py2.py3-none-any.whl (74kB)
Collecting ipython (from jupyter-latex-envs>=1.3.4)
  Cache entry deserialization failed, entry ignored
  Downloading https://files.pythonhosted.org/packages/75/74/9b0ef91c8e356c907bb12297000951acb804583b54eeaddc342c5bad4d96/ipython-7.5.0.tar.gz (5.1MB)
    Complete output from command python setup.py egg_info:
    
    IPython 7.0+ supports Python 3.5 and above.
    When using Python 2.7, please install IPython 5.x LTS Long Term Support version.
    Python 3.3 and 3.4 were supported up to IPython 6.x.
    
    See IPython `README.rst` file for more information:
    
        https://github.com/ipython/ipython/blob/master/README.rst
    
    Python sys.version_info(major=2, minor=7, micro=16, releaselevel='final', serial=0) detected.
    Your pip version is out of date, please install pip >= 9.0.1. pip 8.1.1 detected.
    
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in c:\users\appveyor\appdata\local\temp\1\pip-build-zf3_j7\ipython\
You are using pip version 8.1.1, however version 19.1.1 is available.
You should consider upgrading via the 'python -m pip install --upgrade pip' command.
=================================== log end ===================================

From what I understand, there is a problem when installing the dependencies. It tries to install Ipython 7.0+ which does not support python 2.7. But this problem is well above my skills for me to try to solve it.
And anyway, the problem does not seem to be related to the pull request itself.

I hope this message will relaunch interest in this pull request.
Thanks

[Tautvis]

Synced with master branch which triggered new build. No more Python2.7 build issues.
Could we merge this one please?

[Tautvis]

Friendly ping

[juhasch]

Thank you and sorry for the long delay.