Fix Procrun crashing and cosmetic installer tweaks

The culprit was our start method was returning right away. A careful reading of the Procrun docs says that under Java or jvm mode, that method must block until stop is called. They deal with *not* doing that properly by crashing on stop, apparently.

Tweak install script to perform file edits using the AfterInstall hook so that the service install and start can be moved to the Run section. This allows progress messages in the normal flow of the installer and should be clearer should it hang again.

Re-enable the selection of an install directory as the core package *does* let you do it, I just missed it before. Select the core's install location for the default.

Lastly, add background and header image files and a conclusion page.