Added progress bar when downloading book, in Sailfish-qml version.
Removed some unnecessary signal emissions in qml version.
Added missing book download progress callback. (Only tested in Sailfish)
destroy() was not called on DownloadBookRunnable on download finished when listener not set. This would lead to a memory leak. (although listener *should* always be set...)
Sailish: Removed the "??????" page header of a books library page.
 +Some clean up in the qml code.