Add a tooltip to each label and image with the description of the pack or mod.

[tintin10q]

This should close #36. For some reason the tooltips only show up if you are not on the first tab of the JTabbedPane. I hope someone knows why that happens so that can be resolved. But if we don't know then this at least ads the descriptions to the other tabs so I think it is still valuable to merge.

I also tried for a bit to add the descriptions in each DataPanel but there was not really enough space for that. It would require the gui to be much bigger.

Another option I thought about is to have a big label or text area above the install button and just put the description of the hovered name or image in that box. But this solution is much simpler.