Remove canLink method

[dominikl]

Removes the canLink method, which only checks if the dragged object belongs to the logged in user, and if it doesn't prevents the DnD action. I wonder why this method was there, because one doesn't necessarily have to be the owner of the object in order to be allowed to move it (see #131 ).

Test: Check the scenario mentioned in the above issue now works.

[jburel]

• User can move his/her own data. The checks are correct
• User with suitable permissions can move other users' data.
• User without enough permissions cannot move other user's data

[jburel]

One RFE. The message could be improved to "you do not have the correct permissions" in
This should be done in a follow-up PR.