[Feature] add menu to chose allowed characters and length for random generator

[mstojanovic]

Why/User Benefit/User Problem

some sites have specific requests on password and the random generator doesnt fulfill the requests wit the generated password

Acceptance Criteria (how do I know when I’m done?)

a user can set a list of characters (i.e. capital, lower, digit, symbol) and length (e.g. a slider with values from 10 to 50) of generated passwords as a master setting and during the generation option in the password field

Not included

[CowsEatGrass]

This would be very useful. The Lockwise App for Android does not generate any passwords at all.