Fix for #1840: we expect 500 server errors to also return JSON messages

Conflicts:
	kalite/distributed/static/js/distributed/distributed-server.js
Change 'change password' button to 'edit account preferences.'

Conflicts:
	kalite/control_panel/templates/control_panel/account_management.html
Show username & points (optional) in sitepoints element; change navbar.

Conflicts:
	kalite/distributed/static/js/distributed/distributed-server.js
	kalite/distributed/templates/distributed/base.html
solve #1956: use decorator-specific wrapper/inner_fn

Conflicts:
	kalite/facility/decorators.py

Conflicts:
	kalite/facility/decorators.py
Fix for #1854: Change "mastery of topics" to "progress report"