OMERO homebrew dependencies

With the recent dependency modifications added to the Homebrew formula, most of the OMERO dependencies are now directly installed and managed by Homebrew. This has consequences in terms of the installation workflow, namely one should be able to install OMERO and most of the required dependencies using:

```
brew tap ome/alt
brew install omero
```

This PR reflects these changes by:
- removing the Homebrew dependency logic from omero_homebrew.sh leaving only the Python requirements (not handlded by the formula yet)
- modifying the installation workflow in the Hudson script accordingly

If the OMERO-homebrew-stable job survives this PR, the documentation page will need to be modified to reflect this simplified installation workflow.

/cc @joshmoore