Emulator Launch, Commands and Extension Tech Debt Buydown

[justinwilaby]

This WIP addresses provides some much needed buydown of tech debt regarding how the Emulator is launched, the extensions infrastructure and the command system.

This PR provides:

1. Decorators for registering a command and a DI container for the command service. e.g.

class MyClass {
 @CommandServiceInstance()
 private commandService: CommandServiceImpl;

 @Command('commandName')
 protected myCommand(args) {
    // Do stuff
  }
}

2. Removal of the ts-loader from webpack which halves the build times
3. Targeting ES6+ in the build and using terser for minification
4. Bumped botframework-config out of preview and into v4.4

fixes #1588

[tonyanziano]

Would like tests for the CommandService, CommandRegistry, and Extensions changes

[cwhitten]

@justinwilaby have we gone through the 4.5 release checklist on this change?

[tonyanziano]