DictTableModel bugfix

[Neverhorst]

Description

Bugfix in the qudi.util.models.DictTableModel.get_key_by_index method. Index was off-by-one. Also improved IndexError message.

Motivation and Context

Resolves #70

How Has This Been Tested?

Load config with one or more modules configured as allow_remote: True and click in manager GUI View -> Show remote

Types of changes

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

Checklist:

• [x] My code follows the code style of this project.
• [x] 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.
• [x] I have checked that the change does not contain obvious errors (syntax, indentation, mutable default values, etc.).
• [x] 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.

[LukePiewalker]

I just tested on my office PC and with remote modules, while starting qudi from the console with two different configs via the "-c" option. The table lists all the modules, with "allow_remote: True", as expected. Just to double check: The column "remote modules" aka remote_module_listview, besides "shared modules" so far is unpopulated, since it is probably not implemented yet, correct?