Move lockfile and compiled css away from repo

package-lock.json file is already put into .gitignore, but it is still inside the repository. For starterkit we should let the people decide whether they want to use npm, yarn or somerhing else. Also it is created with some older version of node and it gets overriden after running npm install locally, which may be confusing.

I would vote also to remove the compiled dist directory out of repo and follow that with a solid statement in the README file saying that you have to run npm build at least once to let the theme work properly. This is a starterkit boilerplate, not a ready theme, so such an approach sounds more adequate. Keeping a compiled dist dir in a repo will also add an unnecessary noise to the git repository and may cause potential merge conflicts.

Putting dist dir into .gitignore makes sense because it encourages a more CI style of work, and also make this project easier to maintain. However, we should put inside a .gitignore a commentary in a following style:

# Ignore compiled assets - remove it if you prefer to commit compiled css into the git
/dist/