Refactoring DNS. Added setters which are mainly used by CLI.
DNS CLI supports editing nameservers.
Updated changelog.

Conflicts:

	VERSION
	package/yast2-network.changes
Merge remote-tracking branch 'upstream/master'

Conflicts:
	VERSION
	package/yast2-network.changes
Merge pull request #44 from mchf/master

DNS CLI supports editing nameservers.
https://fate.suse.com/312733