Improve FastTable and extend its possibilities

FastTable was integrated into Pharo 5.0 to solve two main problems that the old lists implementations were facing, first the performance issue, old list’s data source was limited to a couple of hundreds of rows only and second the lack of extensibility since old lists don’t handle complex element morphs very well. Since their integration, FT and their subclasses have known several improvements allowing them to render multi cells tables, expandable trees and draggable lists but the development is still in its early stage and there are still a lot of work ahead. The goal of this project is to target the needed improvements and extensions to build a better FT family widgets that could fulfill much bigger variety of applications.