Filter functionality of control flow view accepted and merged in TMF

This feature is comprised of two parts.
The first part is the backend work that allows to hide rows in the control flow view.
The second part consists of a dialog that lets the user select which rows to hide/show.
When visualising or analyzing a trace, only some processes are important or interesting. Some processes are from system or secondary tasks and are not interesting to the problem being investigated. By hiding these processes, the control flow view is less cluttered and it is easier to navigate the view without having to scroll vertically.
This patch is my first major contribution to TMF.