progress towards impression and click stats on all sources, plus some internal cleanup

(framework portion)

suggestionCursor has new callbacks for impressions and clicks
- impressions now used to trigger "more" UI, cleanup apis around that

search dialog reports which position was clicked on via cursor#respond
- can now detect when sources under "more results" are clicked
- also used to simplify existing stuff:
  - can detect when "more results" entry is clicked and toggle base on that (no longer need INTENT_ACTION_CURSOR_RESPOND one off)
  - use response from click reporting to instruct which position should be selected