Added test cleanup listener to detect untidy tests

After each test suite, detects whether there are stray datafiles, hooks
or proxies, then show a warning and clear them.
Fixed apps loading order

On SQLite the app order can be arbitrary and cause strange bugs.
On MySQL, the app order seems to be always alphabetical.

This fix enforces alphabetical order to make sure that all environments
behave the same and to reduce bugs related to app loading order.

Fixes #6442
fix preview for reshared file
Made password field required on client side

Fix for case described in https://github.com/syncloud/owncloud-setup/issues/19
[tx-robot] updated from transifex
Merge pull request #6554 from owncloud/fix_5982

fix preview for reshared file
Merge pull request #6561 from syncloud/master

Made admin password field required on client side
Merge pull request #6449 from owncloud/core-appsorderfix

Fixed apps loading order
Merge pull request #6520 from owncloud/tests-testcleanuplistener

Added test cleanup listener to detect untidy tests
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
[tx-robot] updated from transifex
Merge remote branch 'upstream/master'