Allow for editing invitee's names after appointment creation

[sander]

Because during creation it will not always be clear how invitees will appear to each other, the initiator should be given the option to edit their names from within the appointment overview. Probably the best way is to make the names editable inline within the table, but if that appears to be hard, an extra 'tool' can be added to the bottom, just like what we did with resending invitations.