Removed release subdecision.

For now we do not need such subdecisions. This is (usually) only applied
for board members, for which we need to model something else anyway.

Also, for this we can use the 'other' type of decisions anyway. Because
the person would actually still be in the given organ.
Added installation reference to discharge.
Implemented getContent() on discharge.
Added members list for organ view.
Members are being removed if they are discharged.