Make DateTimeFormatter a service and adjust tests that have been inaccurate

Equivalent to addVendorScript und addScript from OC_Util

* add addVendorScript & addVendorStyle
* refactoring of addScript and addStyle
* add shortcuts vendorScript and vendorStyle

remove translation.php

Added addTranslations and fixed de.js file

Fixed de.js to use OC.L10N.register() and use to correct expected
format.

Added JS unit tests for OC.L10N class

Include translations JS script for all apps

adding argument deleteSelf to rmdirr() - if false the directory itself will not be deleted only it's content

adding repair step to clean the asset cache after upgrade + coding style adjustments

* test case added to avoid adding them later

This fixes some scrutinizer issues.

This patch was automatically generated as part of the following inspection:
https://scrutinizer-ci.com/g/owncloud/core/inspections/cdfecc4e-a37e-4233-8025-f0d7252a8720

Enabled analysis tools:
 - PHP Analyzer
 - JSHint
 - PHP Copy/Paste Detector
 - PHP PDepend

This reverts commit 6254f0a4.

Added default value for $fromTime to prevent missing argument errors and
keep backward compatible.

Changed method signature of relative_modified_date template method to
make it possible to add a fromTime to compare with, mostly to make it
possible to test it.

Added unit test for date and time cases.

Improved the template function relative_modified_date by adding an
optional dateOnly argument which will output "today" or "yesterday" or
"x days ago".

Conflicts:
	lib/private/vcategories.php