fixed undefined method (bnc#872012)

- 3.1.29
Merge pull request #42 from yast/feedback_fix

fixed undefined method (bnc#872012)
use simple "Registration" title
display base product name
remember the entered email and reg. code

and display it when going back

also make the input fields disabled when already registered during installation
added inline help text for registering input fields
use standard check boxes instead of MultiSelectionBox for addons
do not add version to product name

SLES12 already contains the version in the label
support only a single base product

(multiple base products do not make sense)
fixed exception
addons - better layout for checkboxes