Optimize TimelineRenderer to not paint invisible items

Check the dimensions of the window being painted to before actually
painting the events and skip invisible ones.

Some primitive profiling using QTime shows that the average time taken
per event in TimelineRenderer::paint() is approximately halved by this
patch when profiling the QML widget gallery example and expanding all
categories in the timeline.

drawSelectionBoxes() is not optimized because the number of selection
boxes is expected to be so small that the overhead of the check might
outweigh the performance gains of skipping events.

Task-number: QTCREATORBUG-9982
Change-Id: I42e533c11e3a17f9d63b61ce5e4192c8f40e1be9
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Doc: remove the Publishing topic

Qt Creator does not have publishing wizards anymore.
Left a short description in the IDE Overview topic and
removed all other information and links.

Change-Id: I3c49648779a19036d200e1dec4f46116197c18e7
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>