[InputParser] Import compressed WIF's

Bitcoinj core currently supports importing compressed
WIFs: btac.es/1uxNKIN

The current parser simply checks if the WIF starts with a
5, which is incorrect. It should check if it starts with
a K or an L, then verify the length.

This commit is untested (unable to compile due to some maven issues)
but should be a basis of all that needs to change to properly
import compressed WIF's into bitcoinj