help codesandbox auto-detect appropriate template

[brumm]

Currently, we're recursively gathering the active file's content and dependencies to build our { files, dependencies } structure. This works well for plain ES6 JavaScript, but not so much for more involved setups, like Svelte or Vue.

Codesandbox attempts to auto-detect an appropriate template by looking for { dependencies, devDependencies } in the /package.json entry in the files object.

We should search upwards from the selected file up to and including atom.project.getDirectories() for a package.json