Make CI green again and remove Python 3.5 from CI

[kitchoi]

This PR's goal is to make CI green again.

Closes #423
Closes #410

I tried my best to limit the scope of this PR, but it was difficult to achieve 😂 .

In summary:

• EDM version is upgraded to use RH7 repository.
• The test failure in Test failure on asserting identity between trait lists #423 is fixed. The test was failing in the first place but the test was not run on CI before.
• Revert half of Add optional demo dependencies to setup.py #386 which caused CI to be run against a released egg of enable instead of local source
• Fix test errors complaining about GuiTestAssistant not being implemented on null toolkit (see this comment).
• Pin dependencies on traits, traitsui, pyface, apptools to released versions.
• Install traits, traitsui, pyface and apptools from EDM, remove Python 3.5 from the CI matrix. (<-- this is a bit opportunistic)

Details:

• First commit makes sure the current source is exercised by CI and we get the same failure in Test failure on asserting identity between trait lists #423
• The subsequent commit tried to resolve missing link for liblzma from libtiff. The issue affects the most recent libtiff egg for RH6 repository. Upgrading EDM in order to use the RH7 repository resolves this issue.
• Avoid Test failure when run with TraitsUI 7.1.0 #425 by pinning released versions of traits, traitsui, pyface and apptools. Further restrict to TraitsUI<7.1.0. I think the issue should be fixed separately
• Fix the error to do with GuiTestAssistant not being available on null toolkit. It came up in the build for FIX: Make font style- and stretch- check case insensitive #405 as well. Not sure why it only started occurring then.
• Revert half of Add optional demo dependencies to setup.py #386 which installs dependencies for running demo examples (it brings in chaco, mayavi etc). Those dependencies bring in the released version of enable, and since then enable CI has not been testing the local source. We don't really need these dependencies for running tests nor for developing enable. It seems reasonable not to install it by default.

On this:

• Install traits, traitsui, pyface and apptools from EDM, remove Python 3.5 from the CI matrix.

This is because many recent releases have not been built for EDM + Python 3.5 any more. Python 3.5 has already passed end-of-life (see #415 too). This step I can revert.

[rahulporuri]

LGTM. Haven't tested the changes to etstool locally though.

[rahulporuri]

also fixes #410

[jwiggins]

LGTM

[codecov-io]

Codecov Report

Merging #424 into master will decrease coverage by 3.81%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #424      +/-   ##
==========================================
- Coverage   32.73%   28.92%   -3.82%     
==========================================
  Files         206      206              
  Lines       18297    18246      -51     
  Branches     2470     2466       -4     
==========================================
- Hits         5990     5278     -712     
- Misses      11929    12641     +712     
+ Partials      378      327      -51     

Impacted Files	Coverage Δ
enable/layout/api.py	0.00% <0.00%> (-100.00%)	⬇️
enable/layout/utils.py	0.00% <0.00%> (-100.00%)	⬇️
enable/layout/linear_symbolic.py	0.00% <0.00%> (-100.00%)	⬇️
enable/layout/ab_constrainable.py	0.00% <0.00%> (-100.00%)	⬇️
enable/layout/constraints_namespace.py	0.00% <0.00%> (-100.00%)	⬇️
enable/layout/geometry.py	0.00% <0.00%> (-94.21%)	⬇️
enable/constraints_container.py	0.00% <0.00%> (-81.49%)	⬇️
enable/layout/layout_manager.py	0.00% <0.00%> (-72.53%)	⬇️
enable/layout/layout_helpers.py	0.00% <0.00%> (-71.43%)	⬇️
enable/coordinate_box.py	32.65% <0.00%> (-34.02%)	⬇️
... and 9 more

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