Removes medianfeerate result from getblockstats.
Adds feerate_percentiles which give the feerate of the 10th, 25th, 50th,
75th, and 90th percentile weight unit in the block.
Checks that all of the one byte type keys are actually one byte and
throw an error if they are not.
Add tests for each type to check for this behavior.
Added functional tests for PSBT that test the RPCs. Also added all
of the BIP 174 test vectors (except for the updater tests) in the
functional tests.
Added a Unit test for the BIP 174 updater test vector.
