Remove old galaxy integration code

We have reimplemented this elsewhere.
Emphasize that Seal will not warn for wrong property names
Correct typo
Wrote suggetions for upgrading from 0.3 to 0.4
Revise how version strings are computed

With this commit, when possible setup.py tries to build a version string
based on the last git commit id and, if available, the commit's tag
name.
Fix MANIFEST.in file
Improve logic to set version
Fix version=xxx argument to setup.py
Change set_version behaviour to either use git tag or git rev id