Adding a force param to context_set_by_condition() that allows previously written contexts to be overridden

- Adding context_active_values() API function for simpler reaction code.

- Using human-readable region names rather than identifiers.

- #393232: Renaming context_ui_admin.inc to context_ui.admin.inc.

#336469: Fixing sticky checkbox for hidden blocks and using more human-friendly labels in block UI. From dmitrig01.

#356960: Fix for context_ui_set() error where an array of IDs are passed. context_ui_set() no longer accepts arrays for the $id
parameter. Reported by loze.

#356626: Adding patch to improve performance and integration with memcache & aggressive caching. From m3avrck.

- #354882: Strict check between node objects when settings node context. From anantagati.

Adding checks and cleanups to ensure that context definitions don't have any empty items attached to them