(Issue25) Align header contents in their own column. We now also stretch column 3 so that the contents are aligned with the descriptive labels without a space in between. Sadly this causes the quit button to be resized to it's minimum instead of sharing the space with the installation button as the installation button is so large that it squeezes the push button.

aheinecke@intevation.de=Andre Heinecke
andre.heinecke@intevation.de=Andre Heinecke
bernhard@intevation.de=Bernhard Reiter
rrenkert@intevation.de=Raimund Renkert
wilde@intevation.de=Sascha Wilde
emanuel@intevation.de=Emanuel Schütze