Customizable toolbar options

This adds configurable options for Toolbar javascript component.
It's mainly intended to override ``modalWidth``, ``modalHeight`` etc.

The {% cms_toolbar_options %} templatetag is only meant for internal use.

The user only need to add custom options to ``CMS_TOOLBAR_OPTIONS``:

```
    CMS_TOOLBAR_OPTIONS': {
        'modalWidth': 1000,
        'modalHeight': 600,
    }
```