Symfony 2.8.*, 3.* compatibility

[sanderborgman]

Fixes;

• In Symfony 3 the option to override the Router class is removed from the config file. Using setClass on the definition resolves this issue. Symfony 3 Compatibility issue. #17
• The Twig loader was missing the implementation of findTemplate which caused issues with the profiler and debug bar on at least Symfony 2.8+. Sf 2.8.6 , multisite-bundle 0.1.1 is breaking the debugtoolbar  #16

[alexandresalome]

Hey, thank you very much for your contribution. I cherry-picked your commit in a bunch of other commits I've made, and added you to contributors/changelog in the project.

I need to make a couple of modifications to this bundle, and I'll release a new version (0.2.0). Thanks for contributing!

[alexandresalome]

I forgot to mention: project is now tested on multiple versions of PHP/Symfony (see here).

Once again, THANKS!