added a nil check when reading the long product name (bnc#875796)

- 3.1.41
Merge pull request #60 from yast/nil_check

added a nil check when reading the long product name (bnc#875796)
get details about SSL verification error, optionally import the failed certificate
start import certificate dialog
initial certificate import dialog
better helps
translator comments
fixed forgotten testing URL
display the import dialog only for self-signed certificate errors
translate openSSL error messages
show also SHA256 fingerprint
small fixes
display CN in the import progress dialog
certificate details