save as local if save to origin fails

We use to ignore ajax errors. The dom updates but changes aren't saved. No warning.

With this change we save failed ajax puts in browser local storage. This turns the border yellow, which is something. Continued editing sometimes works.

I know of two cases where the server fails.

1. The Persona login expires. The server rejects updates but the client doesn't notice. 
2. The Ruby flat-file update leaves trash after legal json. All subsequent reads and updates fail.

For both cases the edit is now saved locally. For both cases a prompt fork-to-origin will fix things up. This requires a persona login, of course. For ruby the file is corrupted but fork-to-origin replaces it without parsing the corrupted file. Whew.

In both cases we should solve the root problems before we say these problems are solved. However, we can never lose by making the client more server failure tolerant. The internet can go down, for example.

In testing I've found that local editing is unreliable when a page is made local by this mechanism. Users are advised to correct cases 1 & 2 asap until our page save logic is either obviously correct or proven so. Soon. Soon.