Play tab: remove obsolete properties + make properties private where possible
creation of tab controllers moved from ApplicationDelegate to MainTabBarController

MainTabBarController is the container VC, so it it is natural to make
it responsible for creating its child VCs. also, ApplicationDelegate has
too many responsibilities, so cleaning it up is always good.
use a navigation controller on Play tab

required so that we can push GameInfoViewController non-modally
use Auto Layout in GameInfoViewController + cleanup source code
replace TableViewSegmentedCell by UISgementedControl in NewGameController

TableViewSegmentedCell no longer works properly in iOS 7. since it can't
be made to work easily (e.g. with Auto Layout), the only client that
used to work with TableViewSegmentedCell now makes use of
UISegmentedControl directly.

since TableViewSegmentedCell is now obsolete, it is removed from the
project completely.
use Auto Layout in TableViewSliderCell

for simplicity's sake, the value label can be enabled/disabled only
when TableViewSliderCell is created; as a consequence, there are now
two distinct cell types
remove obsolete class TableViewTextCell