downloader: This is the beginning of a rather large rewrite

downloader: This is the beginning of a rather large rewrite

The downloader code has become very complicated because we have large
functions that perform everything at once.

This patch splits a lot of functionality into smaller steps which are
easier to handle, allow better expansion and so on. You know?

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>