Presentations are not intuitive

[Jonathan Corwin]

Presentation apps are disabled by default, and it's a bit daunting and unintuitive to enable and then open a presentation, especially since a restart is currently required but user is not made aware of this and the dropdown to select a controller could confuse.

Suggestions to fix:

1. If presentation controller enabled setting is not present (i.e. on first run), default to Enabled.
2. If a presentation controller is disabled, close down application and update Media tab dropdown immediately. Vice-versa when enabled. Remove the need to restart OpenLP.
3. By default hide the controller selection from the Media Tab. Provide an option on the presentation settings tab to display.