Refactor: Easier support for chains with multiple genesis assets

[jtimon]

Replaces #164 .
See documentation there.

Dependencies:

• HF: Genesis block includes fedpegscript HF: Genesis block includes fedpegscript and signblockscript #187
• Remove CChainParams::bitcoinID Remove CChainParams::bitcoinID #188
• HF: Move block.proof.challenge to Consensus::Params::signblockScript HF: Move block.proof.challenge to Consensus::Params::signblockScript #189

[jtimon]

Rebased after #187 was merged for clarity.

[jtimon]

Rebased

[jtimon]

Rebased to get the travis build.
But probably this will be closed after #260 has been merged.

[jtimon]

@instagibbs I'm still very early in review of #260 but it seems the pegged asset is issued and can be issued further after genesis so there's no need to support several genesis assets as this PR proposed, as far as I understand, one could create a chain with 100 pegged assets (even if mutli-pegged-asset is not supported in the interpreter and the rest of the 2wp componenets yet) and there's no need to put anything in the gensis tx besides a single unit of a single genesis asset since that used once to create a second asset is enough entropy as long as you don't destroy the genesis asset and all the other assets created after it. Besides tahat destroying it is fine, but the point is it should be possible to use it only once and and destroy it.

And because of this text wall, closing, this should be no longer necessary.