Rename Monodroid and Monotouch to Android and iOS

This PR renames all *.Monodroid and *.Monotouch projects to *.Android and *.iOS which are more clear and bring consistency across all projects in RxUI.

## What else?

Because I was unable to open `ReactiveUI_VSAll.sln` without it blowing up with an AccessViolationException in Xamarin, I also made some modification to the project files of the Xamarin projects. Although I am unsure what fixed the problem, in the end it started working again.