support message header collapsing

* toggle header collapse/expand
* initially render read messages collapsed
* collapse removes attachments footer and stops loader
* expand creates/reuses attachments footer, but ONLY if visible
* can (mostly) expand/collapse details
* can expand/collapse quoted text
* add lots of logging (disabled during scrolling!) to catch
  strange layouts

Change-Id: I73f533c91d24ef1c05919d0a3b396f276898107a
9 files changed