Ensure that tab bars are included in accessibility paths. (fixes #41)

`UITabBar` is a class that forces its instances' presence in the accessibility hierarchy
even though they are not themselves accessible elements. Without including it in the
hierarchy, tab bar buttons could not be manipulated by Subliminal.
Adjust wait delay variability intervals to account for both tapping _and_ tappability checks.
Merge pull request #42 from inkling/jeff/match_tab_bar_buttons

Ensure that tab bars are included in accessibility paths. (fixes #41)