lib: download: progress: refactoring: new functions 'assert{,Max}ParamCount'
lib: internal: debdeltahelper: getDownloadInfo: refactoring: avoid using FORIT
lib: internal: debdeltahelper: fix generating right URIs (by using original installed version)

This was a regression from the commit '366b08db'.
lib: download: progress: implemented new 'ui-size' message support
downloadmethods: debdelta: pass delta size (when/if known) to download progress