Added very simple Grunt configuration to check ONLY app.js at this stage...

Initial changes to fix "[More consistency in code #158](https://github.com/joemccann/dillinger/issues/158)". In order to implement full consistency however all files will need to be added.

To use, make sure that you have [grunt-cli](https://www.npmjs.org/package/grunt-cli) installed as global

    npm install -g grunt-cli

Then type `grunt` from the terminal.

The current jslint options being used are:

``` JavaScript
indent: 2,    // Indentation should be 2 spaces.
node: true,   // Expect code to be run in node
white: true,  // Don't worry about white space being exactly as per
              // what jslint would normally expect
sloppy: true, // Don't expect "use strict"; pragma
nomen: true   // Allow initial or trailing underscore characters on
              // identifiers
```
    
At this time, the only file being checked is app.js but if the options are OK then we add in the other files in the project as well.