Update Eclipse/Maven rules to be closer to Gerrit

This includes some fixes for artifact names and layout from recent
buck versions, which will fix project generation. Pulled in some
additional refactorings so the diff between this and Gerrit's
tools/eclipse/project.py is limited to Gerrit-specific things
(top-level target names, GWT, plugins, etc.).

Change-Id: I44411dbee624a68fff9900559277039b5c7b04f2
4 files changed