Fix remember last used path

See #88
Allow the user to open multiple files at once

Fix #88
Add a comment
Fix missing submenus on OS X

CMD+F will now work!
Fix #92
Improve fix #92

Use a time stamp instead of a hash (because the backend is multithreade and two identical lint method threads might running at the same time and thus working with the same hash).

Also cleanup temp files when the compilation command has finished.
Integrate master branch

Conflicts:
	open_cobol_ide/controllers/edit.py
	open_cobol_ide/linter.py