Merkle-block and merkle-tree classes and methods are pretty much stand-
alone and can be moved with no efforts.
Also move the relevent unit test to qtestlib.
We used various ways to enable new features over the last 10 years.
We can remove that legacy code and just set the blockheight.
This cleans up the code quite a bit.
The "UAHF" one used to be "more equal", mostly just because it happened
to be the first.
This makes them all equally equal.
Specifically this removes the special casing and the enum for the 201708
HF (aka BCH fork-point).
We select the right branch now purely based on the historical check-
points.
Remove no longer useful options;
* chain (sorry, supporting the btc chain just doesn't seem worth it)
* initiatecashconnections, we only allow Cash connections now.
* flexiblehandshake, same for incoming. Reject non-cash ones.
TomZ