More flexibility for the QML profiler timeline

The growing complexity of the timeline view makes it harder and harder to navigate. It would be nice to have the following extra features:

• Allow categories to be "shaded", so that only the topmost, empty row remains
• Allow categories and rows (in expanded state) to be reordered by dragging and dropping
• Allow categories to be flipped upside down so that one can get a common base line for e.g. QML and JS call chain.
• Allow rows to be resized vertically so that event heights show more prominently.