More robust setting of data on UserLog, corrected use in generaterealdata, avoid coachreport commands running on central server (BAD)

Conflicts:
	kalite/main/models.py
be able to generate fake coachreport data
hi PDB, nice to meet you, my friend.  NOW GO AWAY.
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into robust_userlogs
needed to increment counters and to sign AFTER setting the counter.
Converting all asserts to ValidationErrors, so that they will be caught and never block actual user behaviors.
Merge branch 'robust_userlogs' of github.com:bcipolli/ka-lite into multiuser_loadtest
make the number of users configurable as well, defaulting to old value (1)