Install nodejs, and client dependencies (via npm).
Add mocha test (in GLClient) to travis.yml.

* Build a glclient package and move to the default directory as intended by
  glbackend
* Run globaleaks in development mode to prepare tests for mocha
* Run mocha.
Maybe it's python-pip to break things.

Python environments in travis are indeed virtualenvs, so we shall:
* install stuff inside virtualenv (no python-pip)
* never use sudo to install with pip
Make clear the separation between frontend and backend in travis scripts.
Do not move GLCLient/build to glbackend.

This path is automatically discevered with -z option.