Expose only extension-api to extensions

Unless a plugin declares "Gerrit-ApiType: plugin" in its manifest,
assume it is an extension and only make the gerrit-extension-api
available to it through the ClassLoader.

For non-plugins, do not make any Guice bindings available from the
server. This further restricts what an extension can see and do with
the system internals.

Change-Id: Ia38336c42786afb1419d64c06b0d908ae92a64d1
8 files changed