Load assets from sub folders

[matb]

Currently adding assets from subfolders of the path setting is not supported. Applications often structure script files in subfolders to allow a better overview (community also asked for this: #47).

The pull request introduces a new parameter recursive. If this parameter is set to true, files from path are loaded recursively. All other mechanism are applied as before. An example usage could look like this:

var assetManagerGroups = {
    'js': {
        'debug': false,
        'route': /\/static\/js\/app.bundle.js/
        , 'path': './public/app/'
        ,recursive: true
        , 'dataType': 'javascript'
        , 'files': [/[a-zA-Z/]*.js/], 'postManipulate': {
            '^': [
                assetHandler.yuiJsOptimize
            ]
        }
    }
};

The parameter is necessary because loading files from sub directories could potentially break existing usages.