Show an animated image while fetching package details (size & version)

Show an animated image while fetching package details instead of the static text "Fetching..." (but fallback into that if there was any problem loading the image).
(I forgot to add these files in my previous commit)
Better handling of command line parameters

I don't think it's neccesary to add a full command line parser for just
one optional parameter, so I did it manually. If in the future we add
more parameters, we can add a more generic parser based on getopt or
KCmdLineArgs.