Granular permissions for vsf_management

Hi maintainer of this amazing module,

For vsf_management we were in need of a more granular permission, so I've created a patch with a couple more permissions.
There is currently no way to give somebody delete file permission without handing them all files permission for all schema's.

• Added permissions for update/delete per scheme.
• Added administer all permission per scheme.
• Added additional docblocks to functions describing attribute types and return types.
• Add 'Add file' local action if vsf_upload is enabled.

The current `all permission` is still working as before, so there's no migration path needed.

Cheers