Added ability to pass custom variables to Handlebars template from Grunt task.

I needed a way to render the current version on the dashboard page, so I created a new option for passing user defined variables from the Grunt task to the Handlebars file. My new Grunt task configuration looks like this:

````
{
        server: {
            options: {
                dashTemplate: '<%= yeogurt.dev %>/dashboard/template.hbs',
                htmlTemplate: '<%= yeogurt.dev %>/dashboard/htmlTemplate.hbs',
                logo: 'images/logo.png',
                generatedDir: '<%= yeogurt.server %>/dashboard/generated',
                userData: {
                    build: 'build.<%= svninfo.rev %>.zip',
                },
                assets: [{
                    cwd: '<%= yeogurt.dev %>/views/components/',
                    src: [
                        '**/*',
                        '!*.hbs'
                    ]
                }]
            },
            files: {
                '<%= yeogurt.server %>/dashboard/index.html': [
                    '<%= yeogurt.dev %>/views/**/*.jade'
                ]
            }
        },
        dist: {
            options: {
                dashTemplate: '<%= yeogurt.dev %>/dashboard/template.hbs',
                htmlTemplate: '<%= yeogurt.dev %>/dashboard/htmlTemplate.hbs',
                logo: 'images/logo.png',
                generatedDir: '<%= yeogurt.dist %>/dashboard/generated',
                userData: {
                    build: 'build.<%= svninfo.rev %>.zip',
                },
                assets: [{
                    cwd: '<%= yeogurt.dev %>/views/components/',
                    src: [
                        '**/*',
                        '!*.hbs'
                    ]
                }]
            },
            files: {
                '<%= yeogurt.dist %>/dashboard/index.html': [
                    '<%= yeogurt.dev %>/**/*.jade'
                ]
            }
        }
    }
````

Notice the extra `userData` option, and how I'm using it to pass Grunt config variables to the Handlebars template. In this example, I can access a string that has the build version zip file in the Handlebars template by using `{{userData.build}}`.
Let's change this to `userData: {},`