Common user visible strings

We're duplicating some user visible strings across plugins. E.g. "App Engine Standard" in both AppEngineStandardWizardPage and com.google.cloud.tools.ecipse.appengine.localserver/plugin.properties/serverTypename

It would be very nice to read these from a single properties file shared across plugins somehow.

Note that the eclipse externalize strings refactoring does not fully accomplish this since it creates properties files in the same directory and plugin.