Plugins with GWT modules need both:
* gerrit-plugin-gwtui
* gerrit-gwtui-common
Export gerrit-gwtui-common in gwtui-api-lib so that only one dependency
is needed to link against in tree plugin build.
This is the same behaviour as when the plugin is built against published
plugin API (we don't publish gwtui-common as standalone artifact).
Change-Id: If8da90dc1038b6d4145d2e2bab333c2642e3c25f
b4edfabc03