Fix JSONObjectField

When pulling data from the db, the JSONObjectField values weren't being
correctly converted back to Python types. Thus you couldn't save some
data, then later pull it out, add to it and put it back in.

This fixes that and tests that were testing against the wrong values.
Merge pull request #382 from willkg/jsonobjectfield-fix

Fix JSONObjectField
Improve display_history for l10n_status

* fix up/no-change/down detection so it works correctly
* add no-change (prints yellow)
* mark movement for locales as well as highlighted locales
* move some duplicated code into a function