Support external config

[gmccullo]

Problem

Love the extension, but it is very verbose. It takes up a lot of space in the settings file. My whichkeys settings has about 2000 lines!

Solution

Let me configure whichkey in a separate file in the .vscode folder (for the workspace) or a user folder. The last one might be trickier. You can have a setting that tells whichkey where its config file is?

[The-Compiler]

Duplicate of #9