FIX: first attempt to clean up EM4x50 commands.

FIX:  first attempt to clean up EM4x50 commands.
 - `lf em4x readwordPWD` merged into `lf em4x readword` See help text
 - `lf em4x writewordPWD` merged into `lf em4x writeword` See help text

 - `lf em4x readword` now download the collected signal data after command.

On device side the lfops.c has gotten some love. Code cleaner,  increased EM_START_GAP from 55 FC to 56 FC, because of how our microsecond(us) clock works with 21.3us increments.

TODO: `lf em4x em4x50read` needs to be factored to use @marshmellow42 's  ASKdemod instead of trying to do itself.