PR: Add a dialog to report internal errors

[jnsebgosselin]

I implemented this as part of another project, so it was not a big job to port the work here and I think it will be quite useful. Ultimately, I want to get rid of the cmd window.

[pep8speaks]

Hello @jnsebgosselin! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file gwhat/mainwindow.py:

Line 28:1: E402 module level import not at top of file
Line 29:1: E402 module level import not at top of file
Line 34:1: E402 module level import not at top of file
Line 35:1: E402 module level import not at top of file