fix 'undefined method' if relnotes_url is empty (bnc#877705)

also distinguish nil and "" in the message
veriosn + changelog
Merge pull request #204 from jsrain/master

adjsuted wording for deploying image (bnc#877666)
Merge remote-tracking branch 'yast/master' into pr/203

adjusting the version and changelog
Merge pull request #203 from yast/undefined-method-empty-relnotes-url

Fixed "undefined method" if an add-on has empty release notes URL
reduced time-out for downloading release notes when behind firewall (bnc#878265)
Merge remote-tracking branch 'upstream/master'

Conflicts:
	package/yast2-installation.changes