added filter button next to packages to compare them to mirror states

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added basic mirror reading implementation to controller

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: added comparison function to compare local package versions to those of mirrors

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
made mirror selectable for filtering of packages

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>