Deletion of EOSIO contract tables

[KevinTuncer]

If you delete the teleport entries with delteles() you have to delete the entries of the cancel table, too. Otherwise new entries in the teleport table can use primary keys which are already taken by the cancel table. This leads to the situation that these entries of teleport table cannot be canceled.

[KevinTuncer]

Deleting old teleports in the teleport and cancel table without violating consensus is now enabled in my pull request #21