Make sure that Scala UID is always a git hash

The value of SCALA_GIT_HASH doesn't have to be a hash. It can be
a branch or a tag too.
Makes sure that we are using a hash as UID.
Updates P2_ID for scalariform and scala refactoring

Since the Scala OSGi bundles are used through all projects, there
is no need anymore to add the Scala IDE UID to the scalariform and scala
refactoring P2_ID.
Merge pull request #24 from skyluc/issue/old-p2-id-computation

Updates P2_ID for scalariform and scala refactoring