Restore travis to a working state.

The following pull requests restores travis to a state where globaleaks gets *tested* but **not** *installed* on a travis environment.

There have been tons of attempt, and tons of different commits adding/removing the same stuff. 
I tried to shrink them as much as possible, keeping them meaningful.
If you are willing to review only a smaller subset of commits, I will do my best to squash them to eventually reach an even smaller subset of commits.
This file at the moment performs three actions:
- clone GLBackend and GLClient (to be removed with #996) 
- add chrislea ppa for npm 
- add torproject repository to install tor. 

I think the latter action is superfluous. Do we really need to install torproject's official version, and not ubuntu's one?