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.

This also makes it possible to unit test each repair step class
individually

This reverts commit 482eded8, reversing
changes made to 354cace1.

Changes a function call in getUserGroups to only retrieve group ids instead of objects.
this change significantly improves performance when using owncloud with many groups, e.g. nested ldap hierarchy (1.2.840.113556.1.4.1941), since getUserGroups gets called in oc_share::getItems, which is needed for every page request.
in my particular case, it took more than 10s to load the calendar page and more than 6s to load the file page.
this was in an environment with 100 user groups (nested) per user. The performance was bad due to the following call stack:
self::getManager()->getUserGroups($user)
  - getGroupObject() (executed for every group!)
     - groupExists() (resulting in many ldap-requests)
since the groups are loaded from ldap, it is unnecessary to check whether the group exists or not.

add a function getUserGroupIds for retrieving group ids instead of group objects. this significantly improves performance when using many (nested) groups.

Sometimes MySQL decides to return the shares in the wrong order, but
some parts of the code seem to require the order to be known, at least
so that the parent shares come before the children shares.

This fix adds an ORDER BY clause to force the order by id.

adding auto increment/PK to table files_trash

adding PK to table ldap_user_mapping and ldap_group_members

adding PK to table ldap_group_mapping

truncate permissions table to allow smooth creation of primary key

adding unit test for creating an auto increment column on a table which already contains data

remove unneeded table files_trashsizes

fix unit test

no need to truncate *PREFIX*permissions

On Oracle adding auto increment columns is not working out of the box - Oracle migrations are to be done manually

Added "dry run" argument to only run the update simulation.
Added argument to disable migration (useful for bigger setups where
table duplication would take too much space)