Merge pull request #29 from rjbijl/master

Added support for an optional 'url' parameter in the 'roots' section
added feature to use a symfony service as a volumeDriver
Merge pull request #30 from sjopet/services

added feature to use a symfony service as a volumeDriver
Fix for calculating elfinder it's maximum allowed height, and solves Maximum callstack problems in some browsers.
Re-added the substraction from elfinder in orde to fit the fullscreen window, modefied the conditional statement so it does not end up in an infinite loop
Merge pull request #32 from wcoppens/master

Fix #31 Uncaught RangeError: Maximum call stack size exceeded in some browsers