add a way for users to add friendly names to their extras models

[ssube]

There are a number of model names built into the client, but that list will never cover everything. It would be nice for users to have a way to add their own labels, either through the extras file or the params file, rather than customize and rebuild the client every time.

[ssube]

This should probably go in the extras file, some additional fields like display and inpaint (for validation), but that means the server will need to load and parse the extras file, as well as sending part of it along to the client.

It may be possible to localize the server-sent strings, if the client has a matching string in their local tables #127, but showing the server strings should be good enough to start.