Various improvements I had locally on my branch

* Add find retainer by address, precisely find retainers of a specific
  closure address.
* Add ArrWords count analysis which performs a census of the ArrWords
  closures.
* Generalise display pane, to allow displaying trees of different types
  (not just ClosureDetails) (used by the arr words census)
* Allow commands to not have key bindings (and just appear in command
  picker)
* Cleanup: Remove "Analysis" modes such as dominator and size analysis.

(cherry picked from commit 349760d0)