feature/yarn-workspaces

[robinloeffel]

• switch out lerna in favor of yarn workspaces
• remove unnecessary dependencies
• remove unnecessary config files
• clean up metadata and file structure

[lbsonley]

check travis build logs for graphicmagick related error. Add it back to travis.yml if needed

[lbsonley]

I think we still need to install graphicsmagick for the image optimization task.

[lbsonley]

we should consider adding multiple node versions here. Travis will do a build for each version listed. I think we should keep all LTS versions of node here. This way we can say we support LTS.

[robinloeffel]

agreed, let's go for 12.x and 14.x

[lbsonley]

@robinloeffel , I forgot to bump the engines prop in package.json everywhere when I did the node upgrade. Since we are updating the travis config for node version, I think we should bump the engines field for all packages.

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