Share password read + write only

[brantje]

Users should be able to share a password to other users in a read + write mode.
In read + write mode, the user can view and edit the password.
This could be configurable per user eg:

User a -> Read only
user b -> Read / write
Group a -> read only
Group b -> read write

[animalillo]

related to #3, mostly the same: password permissions :P

[brantje]

Working since commit 1a1cf3e