1. Allows it to use the more secure CSP rules of the AppFramework.
2. Adds some unit tests.

For #19788

Unfortunately only PHP 7…

This reduces a lot of the autoloader magic and makes sure that we
generate full paths in the autoloader.

OCS -> ShareManager -> DefaultShareProvider

* Added sharemanager class

This is the central class where all API calls talk to (OCS/Activity).
This in turn talks to the share providers to get the actual sharing
done.

It uses all ShareObjects

* Added share class

Simple class to hold all the share properties that is passed around

* Added IShareProvider interface

Interface that providers os a share have to implement.

* was removed in 3e84f170

* used only for windows support
* windows support was dropped in 8.2.0 - see #17379
* was introduced in fd8cb997
* ref #18935