Plugin loading

[samuelthomas2774]

• Patch Module._load to allow plugins to require the plugin API when they load instead of having to wrap every module in a function:

  // index.js
  const Plugin = require('betterdiscord/plugin');
  const SomeComponent = require('./component');
  
  module.exports = class extends Plugin {
      // ...
  }

  // component.js
  const { Vuewrap } = require('betterdiscord/plugin-api');
  
  module.exports = props => {
      return Vuewrap('somecomponent', {
          // ...
      });
  }

• Add a function to the plugin API to unload everything it keeps track of
• Check external module versions
• Allow plugins and external modules to expose multiple versioned APIs

[zerebos]

I like this change, something I wanted to do for awhile. I am at work now so I've only skimmed through it, but I don't see any huge issues. I'll take a closer look tonight when I get home.