iOS Improvements: Table View Source

This PR adds a number of helpful extensions to the UIKit code, extracted from [REDACTED].app

This adds:
* Reactive versions of common UIKit classes, such as UIImageView
* A way to bind ICommands to UIControlEvents
* A TableViewSource that attaches to a `ReactiveList<T>`

## ReactiveTableViewSource

This class is a pre-canned DataSource for ReactiveLists - currently, support for editing or reordering isn't supported, but multiple sections are supported.

## TODO:

- [ ] API Review
- [ ] Docs