Make lots of improvements!

* finish login functionality
* implement highlighting of actual page in menu
* write the language lines for the menu
* implement turbolinks
* implement minification of assets
* switch from Smarty to Blade since Blade is now extendable (last time I checked this it wasn’t, or at least it was not in the documentation)
* switch to bowerphp for asset management
* other little improvements...

Please note that this commit is way bigger than it should be, so I probably forgot some changes. I’ll try to make commits more often from now on.