don't reset package selection

in the installation proposal when partitioning is changed

(bnc#831875, port from SLE11 bnc#450786, bnc#371875)

see commit d1cce0e5a5
fixed slideshow initialization

in add-on workflow the initialization was called too late resulting
in still 0% total progress during whole installation

(bnc#831875, port from SLE11 bnc#663301)

see commit a1772b138d
do not skip package proposal when the partitioner has changed proposed packages

i.e. add snapper packages after switching to btrfs
(bnc#831875, port from SLE11 bnc#704127)

see commit 6c48fd7761
improve the progress bar during package installation slideshow

(bnc#831875, port from SLE11 bnc#724486)

see commit 2be99dd9ff
REGISTERPRODUCT from content file moved to control file

to globals->require_registration

(bnc#831875, port from SLE11 FATE #305578)

see commit 7d9a51bb4a
improved addon file handling

(bnc#831875, port from SLE11 bnc#815899)

see commit 3490193186
3.0.5
Merge pull request #23 from yast/bnc_831875

Merge fixes from SLE11 to master (for SLE12) (see bnc#831875)