Remove unnecessary parameter
Fix NPE when adding a new Server
Move Spacer-URL and Maven Artifact on to AbstractRemoteAction

This way ActionReplace does not inherit these.
Implement checkout action

It can be used to checkout projects from their source. Also add initial
support for checkout out server configuration. It's currently unclear on
how to properly pick the tag (client side support not implemented yet
for this reason).
Render the checkout into a distinct deployment actions

This is basically a faked deployment action depending on the properties
set on the server.
Regenerate metamodel