Update enable password handling

[arifogel]

Includes part of #466

[dhalperi]

suggest defining fragments for Base 64. Something like this modulo antlr repeating syntax {}

F_B64Char
:
    [a-zA-Z0-9+/]
;

F_B64CharQuad
:
    F_B64Char{4}
;

F_B64FinalQuad
:
    F_B64CharQuad
    | F_B64Char{2} '=' '='
    | F_B64Char{3} '='
;

F_B64
:
    F_B64CharQuad* F_B64FinalQuad
;

[dhalperi]

It looks like the pattern is
$ sha512 $ number $ base64 $ base64 space

for the sha512 token

followed by [woldj4] whatever that is.

[dhalperi]

"i think i have to get rid of variable_password" -- you.

[dhalperi]

Approved with a question.