OutputGroup will handle the fee and effective value computations
inside of Insert. It now needs to take the effective feerate and long
term feerates as arguments to its constructor.
Instead of having callers set the fees, effective values, and filtering
of outputs, do these within OutputGroups themselves as member functions.
m_fee and m_long_term_fee is added to OutputGroup to track the fees of
the OutputGroup.
Moves the current coin selection algorithm out of SelectCoinsMinConf
and puts it in coinselection.{cpp,h}. The new function, KnapsackSolver,
instead of taking a vector of COutputs, will take a vector of CInputCoins
that is prepared by SelectCoinsMinConf.
Changes CInputCoin to coinselection and to use CTransactionRef in
order to avoid a circular dependency. Also moves other coin selection
specific variables out of wallet.h to coinselectoin.h
