docs: installation on Ubuntu

I took some time to actually test the INSTALL process (Ubuntu 13.10) and explain some bits here and there. IMHO, there should be a link _Installation_ on the documentation, _First steps_ confuses me.

* tested the installation process on Ubuntu Saucy (13.10)
* ~~disabling redis-server and flower in Procfile (so it matches INSTALL)~~
* removed the trac-related informations from _git workflow_.
* 100% more pygments