Fix for #9422
The file providing the sftp:// scheme needs to be included manually.
Add short description explaining how SFTP ext storage class works.
Added mountType attribute and adapted Delete action text

Added mountType attribute for files/folder to indicated whether they are
regular, external or shared.

The client side then adapts the "Delete" action hint text based on this
information.

Only the mount roots must have the delete icon hint adapted.
To make this detectable on the client side, the mountType can now
be null, "shared", "shared-root", "external" or "external-root".

This also gives room to icon customization on the client side.
Merge pull request #9605 from owncloud/sftp-missing-streamwrapper

Re-add missing sftp:// stream wrapper
Merge pull request #9572 from owncloud/deleteunsharetooltip

mountType attribute + delete hint fix
Merge pull request #9539 from enoch85/patch-1

Fix for #9422
- Added test to trigger index id error
- re-enable encryption migration tests
- sqlite requires reconnect after schema changes