Code refactoring and various improvements

I know that these changes are important and I doubt that it does not will pass as pull request ! But I tried anyway!

### 0.9
* Code refactoring (PHP5, cleanup) (CAUTION: Renaming many methods !)
* Fix admin bar actions with constant VARNISH_HIDE_ADMINMENU
* Hide Varnish Version selector when global $varnish_version is defined !
* Better compatibility with domain mapping plugin
* Use capability instead user level