Merge systray icons

Also, catch a possible problem with the login answer from the
webapp and display a proper message
Save the provider used for EIP as the default provider.
Merge remote-tracking branch 'chiiph/feature/selected_provider_config' into develop
Merge remote-tracking branch 'chiiph/feature/merge_systray' into develop

Conflicts:
	src/leap/gui/mainwindow.py