[Enhancement] Add yarn as a pkg manager.

[emoralesb05]

Feature Request

Look into https://github.com/yarnpkg/yarn and use it inside covalent.

[emoralesb05]

Some nice docs on usage: https://yarnpkg.com/en/docs/usage

And command comparison between npm and yarn: https://yarnpkg.com/en/docs/migrating-from-npm

[joshwiens]

Already using this on my fork, install is faster as you would expect. No breakage from changes in packages due to the deterministic nature of yarn.

Throw in a little guidance on how far you want this yarn'd i.e just the lock, lock + travis, "all the things" and i'll throw up a PR.

[emoralesb05]

Awesome @d3viant0ne ! For now i think just the lock + travis would suffice. 😄 Since i still need to dig into yarn and see all the things we can leverage from. (im still a noob around it haha)