Allows SelectCoinsMinConf and SelectCoins be able to switch between
using BnB or Knapsack for choosing coins.
Has SelectCoinsMinConf do the preprocessing necessary to support either
BnB or Knapsack. This includes calculating the filtering the effective
values for each input.
Uses BnB in CreateTransaction to find an exact match for the output.
If BnB fails, it will fallback to the Knapsack solver.
This is a parital backport of Core PR10637 : https://github.com/bitcoin/bitcoin/pull/10637/commits/6a34ff5335786615771ca423134a484b04831c4e