Test for GET /recording/X/edit
Add a new timestamp via formset

Have tested these cases manually (need test-cases):

- update existing times but add no extra timestamp
- add extra timestamp
- add invalid extra timestamp (e.g. not-ordered) raises error
Allow insertion of timestamp at arbitrary points

e.g. relax constraint on timestamps being ordered.  We still
check that no two timestamps are identical however.
Fix test assumption
Test adding timestamp after, in between, and before
Test changing speaker
Suppress delete for extra formset forms

this will (eventually, hopefully) be obsoleted by
https://code.djangoproject.com/ticket/9061 but
until then, some Javascript!