Add grunt.js project file

Since last year, [grunt.js](https://github.com/gruntjs/grunt) is very quickly becoming the absolute standard "build system" for client-side JavaScript apps. This will certainly be a fine tool to fulfill our minification, deployment etc. needs.

The pull request includes a very simple Gruntfile which allows you to spin up a development server at port 8000 with `grunt server`.

Note that this uses grunt.js 0.4.x (`npm install -g grunt-cli`) rather than the "stable" (but nearly obsolete) 0.3.x version. Also, make sure to run `npm install` in the webclient root directory, otherwise it won't work.