editpw: new features; rmpw: bugfix

- editpw now has a settable password length via
  a "pwlen <num>" command.

- editpw now has a "new" command for the password
  field input that generates a new random password.

- editpw cleanups: new pw_len property and
  overridden preprocess_input method, overridden
  constructor function to initialize new fields,
  password generator factored into a method, redo
  convoluted code in process_input.

- Fix bad import statement in rmpw.