New views 'initializeEngine' config option

Hello,

I am using Ejs to render templates in an application.
I have added an optional 'initializeEngine' function in the config, to be able to tweak an engine, in my case to add helpers support.
```js
views: {
  engines: {
    html: {
      module: 'ejs',
      initializeEngine: function(engine) {
        // add helpers support
        engine.module.registerHelper = function (name, fn) {
            engine.module.filters[name] = fn;
        };
        return engine;
      }
    }
  },
```