Dissolve "expanded" state of timeline

The "expanded" state of the timeline categories is useless most of the time. It's supposed to show a breakdown of different event types. However, there are some serious problems with this approach:

• Most of the time event types represent something like functions or specific code locations. Those can occur multiple times in the same stack. Therefore, multiple events overlap in the expanded view. This is readily visible when JavaScript functions are called recursively.
• The list of event types can be very long. A complex program can easily contain on the order of 10000 different functions or code locations. Navigating this in the timeline makes no sense.
• The ability to resize a row is currently tied to the "expanded" state because the labels on the left are only shown in expanded state. The labels again expose the handles to resize the rows. This is unfortunate. At least the handles should always be shown.
• The expanded state renders slower than the collapsed state as the events are generally spread across more rows which means more separate blocks of geometry to be uploaded to the GPU.
• The geometry for the timeline is currently the most memory intense piece of data being created per trace. The expanded state duplicates that.