New `graphman` command for clearing the call cache for a given chain

[tilacog]

We could expand the graphman chain command with new tasks that deal with the call cache.

For instance, the following command:

$ graphman chain call-cache remove <chain-name> --from <block-pointer> --to <block-pointer>

Would delete rows from the call cache between the blocks specified by the --from/--to block pointers.

If omitted, the absent pointers would be interpreted as open ends of an interval, potentially allowing the invoker to truncate the entire call cache.