Local entity updates

[seadowg]

Blocked by #5923

Entities updated by a local update form are up to date in a local follow up form without submitting.

Notes

There's currently no spec for how an Open Rosa server/Central will signal to a client that a media file is an entity list so Collect won't know what secondary instances to treat specially without a registration form creating local entity lists. So that we can work on this issue before that's created, we could introduce a way of manually adding an entity list through our experimental entity browser.

Local entity updating should be disable-able from Experimental.