Long lived tx coordinators live too long

Currently we support long lived tx coordinators, the idea behind this is to be able to assign coordinators to clients that can live as long as the client is connected and execute many transactions for that client.
https://github.com/SyncFree/antidote/blob/master/src/clocksi_interactive_tx_coord_fsm.erl#L97

Two issues:
Long lived tx coords never die.
They use registered names which we can run out of (i.e. run out of atoms).

Possible solutions:
Use a pool of tx coords.
Assign long lived tx coords with the connection state, so they live and die with the client connection and don't use registered names.