*REVIEW BUT DON'T MERGE* Revision dash revamp

There are two issues that I'm aware of at the moment, and I'd like a pythonista's thoughts on best handling them:

1.  Via HTML5, I am validating the date with an attributes, but someone could put an invalid date in the querystring, and that presently throws a 500.  I'd love some advice on restructuring the view to avoid this issue.  Remember that the results will be served up via AJAX.

2.  In `revision_diff_table.html`, I added a "show_controls" conditional so that I wouldn't have to build those button URLs on the client side.  Brilliant, right?  The problem is that if from "/en-us/dashboards/revisions" the user calls "/es/blah/blah" to get that content fragment, the button text is in Spanish and not English.  :(

Any advice would be appreciated!