R1:149efe68ab61

Improve usability of DarkConsole settings

Summary:
Fixes T3632. Cleans up a bunch of DarkConsole stuff:

- The config setting had out-of-date instructions. Modernize the instructions.
- The setting was sort of hidden under "Display Preferences". Move it to a new "Developer Preferences".
- The setting magically appeared if DarkConsole was enabled on the install. Instead, always show it but explain why it isn't availalbe.
- When the user enables the console, also force it to actually be shown.