Indicate the "unzipping" stage/progress of a package

[SpiritQuaddicted]

I just noticed that if you install a big package on very slow I/O (a dumb virtual machine in my case) the Injector might seem to hang while unpacking the zip. It would be nice if the progress bar that shows the downloading progress could indicate "unpacking" when that is being done.

[hrehfeld]

• check if unzipping is threaded
• show progress of unzipping