Replace Makefile with Grunt

Grunt is more common for JS projects and easier for people to help.

This PR completely maps the Makefile to Grunt.

Just run `npm install` then `grunt` and whatever you would have used with `make`.

Supported commands:
`grunt` - does same as `make`
`grunt heroku` - same as `make heroku`
`grunt scrape` - same as `make scrape`
`grunt test` - same as `make test`
`grunt clean` - same as `make clean`

There are more commands as you can run all tasks that are configured, like `grunt shell:heroku` but it's not recommended.