Merge pull request #2287 from learningequality/nalanda-rct2

Nalanda rct2 into central-master
Safely continue if deleting default_language fails before creating again.
Merge branch 'nalanda-rct2' into central-master
Directly import sha_constructor from hashlib to avoid Django warning.
Add software update link to overview page.
Tweak style and wording on software update page.
in coachreports/urls.py: use \w instead of \d for getting the test_id
in coachreports/urls.py: use \w instead of \d for getting the test_id
Display more details about sync job status on device page.
Merge branch 'nalanda-rct2' of github.com:learningequality/ka-lite into nalanda-rct2
Merge pull request #2296 from learningequality/central-master

A few changes from central-master
Merge branch 'nalanda' of github.com:learningequality/ka-lite into nalanda-rct2
Merge branch 'nalanda-rct2' into nalanda-rct3
Merge branch 'nalanda-rct3' of github.com:learningequality/ka-lite into nalanda-rct3