Categories: Retrieve, adapt and manage categories

Initial patch for category adaptation. Includes the following components:

* CXCategoryTool
    Manages api requests
    Adapts categories
    Stores source, adapted and target categories
    Initializes UI widgets
* CXCategoryCounter
    UI widget for category count at top of column
* CXCategoryListing
    UI widget for category listing at bottom of column
    Handles removing and adding adapted categories

Bug: 66666
Change-Id: I93b6fc0282e087b29079f59d518ee0fb1c4f6408