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
GUI: post instance name in RT reports

- If user submits error report, paste also name of Perun instance.
- Value is stored in /etc/perun/perun-web-gui.properties as
  perunInstanceName=[some_value]
  If not present, "UNKNOWN INSTANCE" is returned.
Merge pull request #355 from zlamalp/instance

GUI: post instance name in RT reports
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.