#125 Update developer documentation to Gerrit 2.8/2.9

[Franz Zieris]

Note: This ticket should probably be on hold until we upgraded to Gerrit 2.9, which was released in July 2014.

Since the update from Gerrit 2.5 to 2.8, the GUI is slightly different. This ticket is mainly about creating new screenshots, but sometimes textual changes might become necessary, too.

Minor cause: The color scheme changed from green to white.
Major cause: Some actions might have another name/another click path and this needs to be checked.

So, to complete this ticket, go through our website, find Gerrit references, check for outdated information (e.g. http://www.saros-project.org/node/141 looks different now), and perform the necessary updates.