add scrypt and make network changes for sexcoin

at this point sexcoind builds, runs, and syncs to block ~155K. That was the
first hardfork where the original retargeting calculation changed.

There is another retargeting algo change at block 572K (KGW) and a KGW fix
at block 643808. The next commit(s) should be for incorporating the those changes.
Create CForkParam class for fork handling code

CForkParams is a blockheight aware class that replicates the CChainParams::Params()
method via CForkParams::ForkingParams() method which will return the proper value for
blockchain parameters which are dependent on the blockheight.

The CChainParams class is linked into sexcon-cli. Adding blockheight awareness to that class
via chainActive usage, causes sexcoin-cli to want to link CChain class which is in main.o.

Linking in main.o drags in everything so to keep things cleaner, CForkParams was created.
CForkParams is linked in with sexcoind only (not required by sexcoin-cli).
Add KGW Retargeting Algo code