Open Contest Details with a modal presentation

This has two major advantages:
  - We properly use a separate navigation controller
    for the push segues within the contest details
    hierarchy
  - We do not need to hide the tab bar when we push
    into contest details. This is generally an
    unsupported operation by apple:
    "Do not modify a tab bar that is managed by a tab bar controller (an
    instance of the UITabBarController class)"