Bug fix on thread error for laser toolchain

[takuya-ulm]

Bug fix on the laser gui, reported in the issue 153:
#153

Description

Missing disconnect() functions were added.

Motivation and Context

How Has This Been Tested?

Followed the procedure in #153.

1. activate gui
2. deactivate gui
3. deactivate logic
4. reactivate gui

Now the error related to the threading disappeared.

Screenshots (only if appropriate, delete if not):

Types of changes

• Bug fix
• New feature
• Breaking change (Causes existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• I have documented my changes in /docs/changelog.md.
• My change requires additional/updated documentation.
• I have updated the documentation accordingly.
• I have added/updated the config example for any module docstrings as necessary.
• I have checked that the change does not contain obvious errors
  (syntax, indentation, mutable default values, etc.).
• I have tested my changes using 'Load all modules' on the default dummy configuration.
• All changed Jupyter notebooks have been stripped of their output cells.

[NicolasStaudenmaier]

For me the PR does not solve the issue as reported in #153. We're waiting for the overhaul of Qudi core which should solve the fundamental problem.
However, it is an obvious improvement of the code disconnecting the widgets on deactivation of the GUI. Thanks Takuya.