Make the transaction history have per-file hints, so we can fix stuff like
http://bugs.freedesktop.org/show_bug.cgi?id=23904 and display deps differently
to explicit files.

installpkgs, update packages should have remove_required

add properties to Transaction interface:
 * bytesDownloaded(u)
 * bytesTotal(u)
 where bytesTotal will be the Full download
 and bytesDownload is how much was already downloaded,
 this way we can easily get how much bytes we need to
 complete our task (total - downloaded)
*** adding this as properties allow us to use it in simulate*
    methods to show exactly how much bytes we need and when
    a transaction is running how much was downloaded.

Transaction::Details
 * If the above (bytes*) properties were added,
   change the size to be always the file size
   (and not 0 if the package is already downloaded
   not installed)
 * Add popularity from 0 to 10 where 11 is unknown
 * Add a stars filter >1stars >2stars >3stars >4 stars

Python backends:
 * Pre-split filters in backend.py, not in each backend.

Transaction::Download
 * Add a boolean 'copy' parameter than controls whether we just download
   the packages to the system cache or to a packagekitd created location.