Once Apple fixes issue with Safari not obeying the localised string,
this *should* fix the issue with the confusing internal version
showing up in the Extensions panel.

Along with changes to Builder, Themes, and the Mac app, closes #148

* Also on iOS (regression – will handle in future commit)
* Removed unused classes

* When the copy of initial data had not completed, the toolbar
  accessory wasn’t showing as we were not completely destroying
  the progress alert modal. We are now.

* *Most* irrelevant menu items now disabled at introduction
* Introduction window now not resizable
* Main window is resizable

* Automatically transition to main app if blocker is already active
* Check in background for blocker activation and immediately respond

* Refactored to move common model code (iOS, Mac) to common project

(And the list of trackers is returned)

…when app was not in focus.