Use R.attr.colorAccent instead of R.color.hot_pink

Bug: 21952435

- To support basic theming of the background and accent colors, refactor
  our usage of the hot_pink color resource where possible to instead
  resolve the colorAccent attribute against the current theme.
- Use BroadcastListener in BaseActivity to update the background color
  whenever the system time / time-zone changes.

Change-Id: I9c736801eb8017cca305fd377628380fef40bfab