Changing RelationshipResolver to use breadth first search.
Travis: Start xvfb for GUI tests.

Tested on #498.
Closes #499.
Catch authentication error with https.

Change the catch logic to throw a MissingCertificateKraken in the case of authentication failure ("System.IO.IOException: The authentication or decryption has failed.").
Show error message for missing certificate in the GUI.
Fix mod list column resize on first repo update
Fix #505
Small fix to get our changes after InitializeComponent();
Revert "Catches DownloadErrorsKrakens gracefully"

This reverts commit baaf92f561f4d2c2f010f3876dc44d21e8aff728.

See discussion on #520 as to why.

Opens #368.
GUI stuff, check description

- Better wrapping for the mod description
- Mark all updated button now greyed out if no updates are available
Better display of provided modules