Fix install script

The original goal was to install an instance of CommCareHQ in a VM so we can build our applications locally as our internet connections is slow and unreliable. I fixed a few things in the setup scripts along the way.

I worked in the branch "master" directly. Please tell me if you need another pull request in another branch.

This pull request makes sure that :
- install.sh script works straight after a fresh install of Ubuntu 12.04 32bits LTS
- localsettings.example.py works straight after a run of install.sh

A quick summary of the changes :
- extra packages are installed if needed (unzip, add-apt-repository and lxml deps)
- couchdb-lucene paths and permission from the tarball are fixed
- pip packages are cached so if something fails during that step we don't have to download everything again
- added vim *.swp files to .gitignore
- changed the DB credentials in both install.sh and localsettings.example.py so they match
- updated egenix pip dependency has the previous seems to not be available anymore
- created a commcarehq PostgreSQL user
- add a commcarehq CouchDB user in install.sh (as one is requested in localsettings.example.py)
- tweaked the README so the webservers are listening to external connexions too