Add sharing mechanism to collections

[mrmn2]

Once #118 is completed sharing collections would be great.

• collections should be sharable with other PdfDing users of the same instance and the public
• When sharing with other users it should be possible to provide read or write access
• When sharing with the public access will be read only

[Blackstareye]

hey :)

i am just curious: what is the status of this feature :) ?

have a great day :)

[mrmn2]

@Blackstareye Sorry, for some reason I did not notice the question. Now that collections are implemented and soon released, sharing functionality will be one of the next things to implement.