Basic CBN auto-complete with classes and declared variables

This PR includes autocompletion on (1) class names and (2) declared variables:
![image](https://cloud.githubusercontent.com/assets/5710686/4354735/731a1594-4241-11e4-98c2-3ce7eaf2a6a0.png)
![image](https://cloud.githubusercontent.com/assets/5710686/4354740/81efccb2-4241-11e4-98a6-6788e0b0e1b6.png)

@Benglin PTAL
@Benglin the idea of referring to the link here is that it is the recommended way of using the "completion window" functionality out of the box by AvalonEdit authors. However, there may be ways of making this more efficient as you suggested. A task has been created for this here: http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4226