Document latest changes to the Homebrew OMERO formula

- Ice (3.5) is now the default version installed by `brew install omero`
- Add options to use old 3.3 and 3.4 versions
- Update PYTHONPATH setting in the configuration section
Add note about SLICEPATH for development server
Add note about .bash_profile
Merge pull request #635 from sbesson/homebrew_4410

Document latest changes to the Homebrew OMERO formula