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- The config setting had out-of-date instructions.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.
- Call out instructions about use of the "`" key more clearly.
Test Plan: Viewed config setting. Viewed settings panel. Changed setting. Enabling the setting showed DarkConsole.
Reviewers: garoevans, chad, btrahan
Reviewed By: chad
CC: aran
Maniphest Tasks: T3632
Differential Revision: https://secure.phabricator.com/D6594
