#4930 added trim of opengraph description to 250

Trimmed opengraph description in mobile view and stream view to 250 chars. SinglePostView still has the long description.

URL used to test (but I also added a jasmine test): http://www.kotzendes-einhorn.de/blog/2014-10/krautstart-die-stimmen-zum-launch-von-krautreporter/

Resolving bug #4930 
I think we can apply some OOP here to enhance future extendability of the constructor:

```js
app.views.OpenGraph = app.views.Base.extend({
  initialize: function() {
    this.truncateOpenGraphDescription();
  },

  truncateDescription: function() {
    // current code of initialize
  }
});

app.views.SPVOpenGraph = app.views.OpenGraph.extend({
  truncateDescription: function() {
    // override with nothing
  }
});
```

Mmmh, does that actually work in JS?