Small adjustments to allow integration with Gerrit Code Review

Hi James,
I've managed to update the Gerrit Code Review plugin to the latest and greatest GitBlit :smile: 

However there are two minor changes I need in GitBlit:
- Logo: the one used in Gerrit could have a slightly different aspect ration from the GitBlit one. For using the same one we need to allow free resize
- IManager injection: with Gerrit plugins the objects are automatically injected and we need to have the ability to start an instantiated manager

Everything else is fine.

Thanks for your time in reviewing this changes.

Luca.