Bug 468504: updates .gitignore to include rts/build

The previously committed .gitignore file includes the build folder.
This folder now has actual content, and should be tracked.  The old
content in this file is now generated in rts/obj.

This also updates the pom.xml to avoid deleting required content as part
of packaging the plugin.  Only the new rts/obj folder is deleted.

Change-Id: Id40d726a03f32d41fb82a6b89c43c9d65c1b1029
Signed-off-by: Andrew Eidsness <andrewe@jfront.com>