Add script for building a custom glclient build and installing it

Should work on debian. Not yet tested.
Import VagrantFile from https://github.com/lastknight/globaleaks_vagrant
Fix vagrantfile
Only backup GLClient to .default if we have not done so already
Add support for adding custom stylesheets

* Cleanup GLClient dir after build
Add support for obtaining the version of GLCLient from the installed globaleaks
Merge pull request #346 from globaleaks/feature/build-custom-glclient

Feature/build custom glclient