Reduce number of categories and minimum size of preferences

Merges the Project, Qt4 and Tool Chain categories into one Build & Run
category, which makes it finally possible to reduce the minimum height
of the preferences dialog.

Change-Id: I8d94aac9c9531200f5d8ca212a53d3edc5734138
Reviewed-on: http://codereview.qt-project.org/5023


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>