Enhance DirtyIndexList to keep track of changed indices and summarize to decent index ranges

[griestopf]

• Assume points are accessed in order of ascending indices
• Store last changed index
• If a new changed index is reported, see if the gap between the last changed index is above a given threshold and decide if a new index range needs to be created
• Find a way to detect and to handle random access (not in order of ascending indices)