Adding support for Strax

[dangershony]

Replaces the initial PR by @zeptin
#278

[dangershony]

Note
federation overrides OP_NOP9 to push fed pub keys to the stack and the
needed signatures to satisfy the federation multisig, to avoid changing
the script engine for now we ignore such outputs and consider them valid
(as was with the opcode OP_NOP9) a malicious node may cause blockcore nodes
to accept invalid blocks however as long as blockcore nodes are minority nodes
its an acceptable risk, users not part of a federation should not really be effected.

@zeptin thoughts?

[dangershony]

All test pass locally