Add pay-to-script-with-state script class

[someone235]

I'm suggesting to add a new script class p2shws, that works as follows:

1. sig script contains <optional other data> <state> <script>
2. The script pub key commits to <script hash> and <state hash> and validates that the witnesses correspond to them
3. Then, the script engine pops <script> and runs it with <optional other data> <state> on the stack.

This, together with the proposed covenant ID scheme, will eliminate the need to bring as witness any data except the previous state to spend a covenant.