Edit section and subsection at course outline page.

WIP.
I'd suggest to move this checks into model? We as result we'll have few helper methods like: `this.xblockInfo.isSequential`, `this.xblockInfo.isChapter`, etc.
Implementation may looks so:
```javascript
isSequential: function () {
  return this.get('category') === 'sequential';
}
``` 
or a bit complex, but more general solution:
```javascript
initialize: function () {
    ...
    _.extend(this, this.getHelpers());
},

getHelpers: function () {
    var helpers = {};

    _.each(['chapter', 'sequential', ...], function (item) {
        helpers['is' + item.toUpperCase()] = function () {
            return this.isType(item);
        };
    }, this);

    return helpers;
},

isType: function (category) {
    return this.get('category') === category;
}
```