Drop yarn support for development (stick to npm only)

[danielcaldas]

This will avoid conflicts and the overhead of maintaining both package.json and yarn.lock. If you are picking up this issue please check out the checklist on this trello card, it should contain all the steps that we need to perform to clean up yarn relative configs.

[sasalx]

Sure I can take it. However, I didn't understand the reason for dropping yarn. Afaik lock files generated automatically so you are only maintaining package.json.

[danielcaldas]

Afaik lock files generated automatically so you are only maintaining package.json

Kind of. In order for the yarn.lock to be updated you need to actually run yarn. Imagine you want to add a new dependency, you go and type:

npm install --save my-dependency

All good, package.json and package-lock.json are updated but yarn.lock is left behind unless you run the same command with yarn (or... worst... you need to do a yarn install to update yarn.lock)

[sasalx]

Oh, I see so the project mainly uses npm and keeps yarn for the sake of it.

[danielcaldas]

Closed with #128