Make abstract Middleware class public

fix mobile and desktop app images looking different

Automatic config can set some of parameters or all of them

More Interfaces for the public api

It doesn't make sense for subclasses to have to implement
all methods.

Allow "Finishing..." button on setup page to be translated.

more elegant style for Personal and Admin settings

upload abortion detection only for PUT

Load all mimetypes in one go

Design fixes

e.g. LOCK would break with this approach

Input simplify

Improved request

Fixes #5130.