__init__.py re-inserted and renamed polibeepsync to common

Import statements have been rewritten to accomodate file name change.
Ok button hides window
Default text for login information label
Add functionality to GUI

* implemented insertRows and removeRows to update the view when new
courses are available or when some should be removed
* load username, password, courses list from "data" file
* testlogin() ensures that the user is logged
* refreshcourses() synces the local state of data with the remote
website
* syncfiles() should be able to download files to local directories (not
tested)
Function to save a folder recursively +  tweaks

The function is not tested yet; other tweaks are

* helper function to get the modification date for a local file
* new courses created default to sync=False
* updated docstring for logout()
Change in filesettings defaults and updated unit tests