Remember provider along with username and password
Check provider api version for compatibility
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
Merge remote-tracking branch 'ivan/feature/2774_check-provider-api-version_rev1' into develop
Merge remote-tracking branch 'ivan/bug/2755_remember-provider' into develop
use twisted processProtocol instead of QProcess to drive openvpn
updated api
Merge remote-tracking branch 'kali/bug/openvpn-process_rev4' into develop