917 duplicate output

[bmuenzenmeyer]

Closes #917
Closes #833
Closes #937 (I think) @piotscig can you confirm when released

Summary of changes:

• Removes obsolete copy logic from the CLI. Core has done this from an early 3.0.0-alpha stage.
• Removes the call to build() before serve(), since serve() does build for us and then they both set up watches, creating problems.
• Implements commander's --no-watch correctly to provide default true with ability to set to false
  • This is a new capability for build and serve commands. For example, now you can serve your PL without watching files.

    npm run pl:serve -- --no-watch
    

[coveralls]

Coverage decreased (-0.01%) to 74.574% when pulling 830c568 on 917-duplicate-output into b89d0dd on dev.