Add support for gas and gasPrice in `tx:nop` and `contract:send`

[fvictorio]

Both should support --gasPrice, as tx:send does.

contract:send should support --gas, as tx:send does. tx:nop could support it too, but it doesn't make a lot of sense (it will always require only 21000).

[zfogg]

+1 when can we get this?