feature: implement strategy of overwrite order tree in state_manager

[lispc]

# finished orders can never be used again
order_leaf_to_overwrite = `select order_leaf where state = 'finished' order by id asc limit 1;`
if order_leaf_to_overwrite is None:
    # oldest open order is less probable to be used later? heuristic 
    order_leaf_to_overwrite = `select order_leaf order by id asc limit 1;`

[lispc]

implemented in the rust repo. Not tested yet