This reverts commit 6a1a4880.

The updater is using "before update" repair steps and "regular" repair
steps.
The "regular" repair steps are also used by the CLI tool.

Currently no steps exist but can be added later in the static methods in
the \OC\Repair class.

Added unit test to test messaging, error and exception cases.

Conflicts:
	lib/private/vcategories.php

the only problem that I found with it so far is that it gives a database locked error on login,
the rest seems to work fine but more testing is required.

Start of the refactoring. Commit is quite big because I forgot to use git right from the beginning. Sorry.