* Split subsetting into `form_preferred_input_candidate_subsets` fuction
* Use `get_input_counts_in_preferred_order` directly from `make_single_transfer_input_selector`
* Input selection policies are passed number of inputs to select for, instead of dynamic
* Filter dust before calling policies
* Throw more descriptive errors when not enough money (could still be improved for not enough input case)
* Replace multiprecision::int128_t with multiprecision::uint128_t for simplicity and cryptonote::print_money
* More documentation
* Remove "select two, prefer oldest" policy for now
