[FEATURE] Add option to run kangaroo with custom password

[matthme]

Add the option to run kangaroo with a custom password. Requires to add logic to the splashscreen to setup / prompt for a password.

• [ ] setup password screen (and determine whether or not to show it or the enter password screen)
  • for now a warning about the fact that password cannot be reset
• [ ] enter password screen
• [ ] error message in wrong password case
• [ ] option in the config file to use/not use password prompt or ask whether or not to use a password
• [ ] write randomly generated password to file that can only be accessed by the owner