Reworked modals... LivestreamerController WIP

Work in progress!
LivestreamerController still needs to be worked on. This means that
streams can't be launched right now.
All other controllers and routes have been changed accordingly.

Got rid of the old ad-hoc implementation of the modals. They now follow
the ember MVC structure, use their own controller (mostly use an
existing controller though) and all control elements are defined in the
template of the modal's view.
Reworked LivestreamerController

Completely reworked the LivestreamerController, so that it works again
after the recent changes to the modals.
Also applied some changes other stuff which is tied to the stream
launching mechanism.
Some fine-tuning of LivestreamerController
Merge branch 'modal-rework'

Reworked modals and stream launch mechanics

* Got rid of the old ad-hoc implementation of the modals. They now
  follow the ember MVC structure, use their own controller (mostly use
  an existing controller though) and all control elements are defined
  in the template of the modal's view.
* Completely reworked the LivestreamerController, so the stream launch
  flow is much simpler now. Also applied some changes other stuff which
  is tied to the stream launching mechanism and also moved the model
  used for running streams into its own file.
* The stdout and stderr messages of the livestreamer child process are
  now parsed and being displayed inside the modal. Also added some more
  error classes with error messages.
* Moved the verification timeout value to the package.json config hash.
* Applied changes to the modal logic of the SettingsRoute,
  ApplicationController and VersioncheckController as well.