added more useful message, only show button if registered.
do not check online status synchronously.  this check is no longer used; it just delays users.
Merge pull request #572 from bcipolli/no_serverside_synchronous_online_check

HOTFIX: No serverside synchronous online check
removing hard-code of playground URL--don't rush so much\!
Merge pull request #529 from bcipolli/force_sync

Mpilonhle: Expose button to force syncing to happen NOW
Merge branch 'release-0.10.0' of github.com:learningequality/ka-lite into release-0.10

Conflicts:
	kalite/securesync/management/commands/retrypurgatory.py
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into release-0.10
less memory-intensive signing and verification of large files.  Future use for signing zip files.
Merge branch 'crypto_large_file' of github.com:bcipolli/ka-lite into friendly_admin
using more memory-efficient algorithm for signing and verifying large zip file.