Add the ability for user role to not alter/delete bookings created by other users.

[iJar82]

For our use of this program we would like the users to create booking for meeting rooms themselves. It should be possible for users to alter and/or delete their own created bookings but not of the ones created by other users.
I know this requires some changes to the database as mentioned in an email by you on my question:
"At the moment there's no database field to record who the event was booked by (as in a user-id or something) so that would need to be added."

[neokoenig]

Requires #47