TableScreen Refactor

This is the long overdue refactor of PM::TableScreen & related table modules. I'm pretty happy with it. Take a look and give me your thoughts if you want.

Biggest changes:

1. Moved all of the spaghetti code out of `_sectioned_table.rb` into three new classes/modules.
2. `PM::TableViewCellModule` sets up individual cell attributes
3. `PM::Table` implements all the UITableViewDelegate & UITableViewDataSource methods
4. `PM::TableData` allows for easily accessing all the table data
5. Fixed the problem with `background_color`
6. Added lots of unit tests
7. Removed legacy reference to `MotionTable`