Make clock larger on tablets

Also fixes "Large text" option on lockscreen and fixes Keyguard
layout on smaller devies. In addition, make sure that landscape
layout for phones isn't terrible broken (it's not pretty but
it works).

Bug: 14994495
Bug: 15589636
Bug: 16799035
Change-Id: I9ab76af41cbecd1a727d019e422765efbbd3276d