Makes task understand native .csslintrc format

Intro:

Currently csslint grunt plugin supports json jshint flavored format for `.csslintrc`, although the csslint itself define own syntax which is plain text with cli flags separated by [whitespace](https://github.com/dmi3y/grunt-contrib-csslint/blob/nativecsslintrc/test/parsecsslintrc/nativeoneline) or [newline](https://github.com/dmi3y/grunt-contrib-csslint/blob/nativecsslintrc/test/parsecsslintrc/nativemultiline). [Next](https://github.com/CSSLint/csslint/issues/359#issuecomment-35819236) version of csslint will support [json](https://github.com/dmi3y/grunt-contrib-csslint/blob/nativecsslintrc/test/parsecsslintrc/nativejson) formatted rc files, but it is not compatible with [grunt](https://github.com/dmi3y/grunt-contrib-csslint/blob/nativecsslintrc/test/parsecsslintrc/taskjson)  defined version.

Reason to PR:

In case to share same options between csslintand grunt plugin (for example to integrate it with sublimelinter, or simply to use it as cli)  we have duplicate them in different files. This could be automated with custom script, but I feel better approach would be to provide multiformat support by either csslint or grunt plugin wrapper. As soon as grunt plugin json format never been part of csslint, I do pr here.

What inside:

- [External](https://github.com/dmi3y/grunt-contrib-csslint/blob/nativecsslintrc/tasks/utils/parsecsslintrc.js) parser which makes possible guesses over which format configuration file is.
- Parse and normalize provided options into grunt plugin version json.
- ~~As side bonus it striped out comments if any of  loose hash  formats provided instead of json (eval instead of json parse).~~
- Unit tests for this functionality as well.