GUI: new logo and gwt version

- Bumped GWT version to 2.6.1.
- Use new logo as backup if not set on server side.
- New favicon and Perun's LargeIcon
Merge pull request #352 from zlamalp/logo_and_gwt

GUI: new logo and gwt version

- Bumped GWT version to 2.6.1.
- Use new logo as backup if not set on server side.
- New favicon and Perun's LargeIcon.