The API activity indicator, which gives users indication that network

communication is occurring, has previously been pretty interwoven with

the rest of the API communication code. This is the first step in

cleaning up that code by moving the display for this indicator into its

own view.
The view manages showing activity and error information, and displays

details on any errors shown, just like the old indicator. However, the

error details box has been simplified, removing the response payload.

That information was more useful back when browsers didn't come with

useful debugging consoles, but is a lot less useful now. Instead of

attempting to show anything, we just say that more details might be

found in the browser and server logs.

Tested Loading/Saving activity indication.
Tested display of errors and error details.