Issue 19

@jorgesilva The AccessibilityNodeInfo class cannot be extended in a newly created class because AccessibilityNodeInfo has no constructor.  So Comparable interface cannot be implemented. An alternative  approach is to add an AccessibilityNodeInfo instance variable in a new class, then implement Comparable.This approach distorts the architecture of accessibility nodes and I don't recommend it.  
I have implemented an insertion sort on node list in TeclaAccessibilityService class in this pull request. Please take a look and comment.  
This pull potentially resolves #19