refactoring to share common code between iOS and tvOS

[kambala-decapitator]

Currently iOS and tvOS have a lot of similar duplicated code. This needs to be refactored to use common code for both platforms. Examples: app delegate, root view controller, GL view.

Also, I suggest to switch to GLKViewController if possible instead of using plain CAEAGLLayer inside custom view/view controller.

[fuzzard]

Is there a point to migrate to glkviewcontroller when both are deprecated in ios/tvos 12?
Easier to just stick with caeagllayer and look at how we bring in metal instead for the long term goal?

[kambala-decapitator]

when Kodi was initially ported to iOS, GLKViewController wasn't available. Afterwards it has been added to iOS SDK to ease dealing with OpenGL surface.

Metal can be enabled almost out of the box with Molten VK as soon as Linux implementation of Vulkan is ready.