Save user preferences

[matthew-white]

The user can make a number of selections/choices in Frontend that we've talked about persisting. We've talked about persisting them server-side. Some preferences seem to be top-level/sitewide, while others seem per-project. We already have sitewide settings (for usage reporting), project settings, and form settings. However, those are not specific to the user. This issue is about saving individual users' preferences.

Top-level/sitewide preferences to persist:

• Whether the top panel on the homepage is shown or not (moved to #719)
• The sort order of the project list

Project preferences:

• The sort order of the form list (moved to #719)
• Whether the form trash is shown or not - Add ability to hide forms trash #690
• Whether managed or legacy QR codes are shown for app users (moved to #719)

[matthew-white]

I've updated the description of the issue to make it clear that @brontolosone's work will close this issue. This issue is about adding a framework for saving user preferences, then using that framework for a couple of specific preferences. There are other user preferences that we want to save, and I've moved those to a separate issue (#719).