Show Progress Dialog For Downloads, etc

It would be good to see a progress bar when things are downloading, such as a package so that a user kind of has an indication that things are still waiting.

Start by tracing how ChocolateyGUI initiates package and other downloads, since the issue names no files, tests, or entry points. Identify the download lifecycle and existing UI feedback, then define completion as a visible progress indication that updates while a download is waiting or running.

Written by the indexing model from the issue text.