iOS - refactor BeagleScreenViewController and ViewModel

[theffc]

This is a quite difficult issue, should be further discussed to better understand how this could be achieved, could actually cause some breaking changes

Goals

• currently our BeagleScreenViewController and ViewModel are quite large (250+ lines) and the logic itself is difficult to follow
• prepare our structure to when initiating a beagle flow, users could show loading and error outside BeagleScreen
  • for this we will need to separate all that logic about requesting and changing view state from ViewModel.
• have tests for ViewModel logic, even if we change that code to other places
• maybe we could remove Bindings logic from ViewController, and have it at another place
• maybe execute actions could be outside of ViewController as well