[experimental] adding applyConfig and yepnope patch to support conditions

This PR adds support for conditions outside of the scope of the current conditions implemented by YUI:

It allows you to apply a condition at any given time, and this condition will dictate how things are going to be loaded.

First, we need to apply a patch (ideally this will be implemented in YUI directly):

```
    app.yui.patch(require('express-yui/lib/patches/yepnope'));
```

After that, we could start calling `app.yui.applyConfig()` on the server and/or client, it doesn't matter much:

```
        app.yui.applyCondition('intl-messageformat', {
            test: function (Y) {
                return !!Y.config.global.Intl
            },
            nope: ['intl-polyfill'],
            yep: []
        });
```

What this does is to add a new entry under `Y.config.conditions['intl-messageformat']` with the conditional object. This information will be consumed by the patch to guarantee that the module denoted by `intl-polyfill` will be attached before `intl-messageformat` if a global `Intl` member does not exists.