Handle missing module errors more gracefully

[callumlocke]

Problem: often I clone a repo just to explore the code in Atom (and I don't want to bother doing npm install, because I'm not actually going to be developing in the repo, I'm just viewing the code). But if the repo uses ESLint, this fires up linter-eslint, and every time I click on a JS file, an error pops up:

A new error appears for every file you view. They keep accumulating until you close them manually. I don't want to have to run npm install just to keep my linter happy in someone else's repo I'm just browsing.

It would be great if linter-eslint could catch this kind of error and just display a small notification in the status bar instead of allowing big intrusive errors to overlap my code.

[IanVS]

We have talked about putting other common error messages in the status bar (#735 (comment)), and I like the idea of doing the same thing for these messages as well.

[Arcanemagus]

Closing as a duplicate of #387.