[ESLint] Support for defining default eslint.json

[letmaik]

I use the same code style in all my projects, so it makes sense to me if I could just configure a default eslint.json file via an absolute path (outside any particular project) in the central preferences, in essence providing a different default than the built-in default of tern-eslint.

[angelozerr]

I will do that when I will find time.