improved require type detection; find package.json in parent dirs and more

- Don't include `var ` statement in multiple var definitions (separated with comma);
- Make a (wild) guess if it's inside array or func call or something;
- Try to find nearest directory containing `package.json` relatively to opened file if there is no such file in current project;
- Allow to omit other file extensions (`jsx` in particular);
- Renamed settings files, allow to create user settings (like other plugins do).
Want to also detect if `let` or `var` is already on the line?