Remember previously used remote to push to

[kriegaex]

This is a follow-up issue for #404, as requested by @uwolfer.

When working with multiple remotes, the push dialogue defaults to origin, even if the Gerrit server's remote is something different, such as review or gerrit or eclipse_review. If the plugin cannot auto-detect the correct server name from the preconfigured web URL in the plugin settings (which would be ideal), at least it should remember the remote I pushed to previously and suggest it again.

[simonschaufi]

Related to #406