Inheritance improvement for editors

Hi,

I made some improvements for `HandsontableTextEditorClass`, `HandsontableAutocompleteEditorClass`, and `HandsontableDateEditorClass`:
1. To keep code clean and safe `HandsontableDateEditorClass.prototype.constructor` is now `HandsontableDateEditorClass` instead of `HandsontableTextEditorClass` (same for `HandsontableAutocompleteEditorClass`)
2. `HandsontableTextEditorClass` is not triggered while setting inheritance, so `if(instance)` is no longer needed in constructor.
3. Calling super methods seems to be much faster when using `.apply`, instead of adding `Child.prototype._method = Parent.prototype.method;` and calling it by `this._method`. Moreover it makes interface much cleaner.
http://jsperf.com/declaration-apply-vs-prototype-reference-vs-super
http://jsperf.com/instance-apply-vs-prototype-reference-vs-super/2