NetworkService: changed API to support more backends (namely wicked)

The change is backward incompatible
Updated changelog
NetworkService: Renamed cur_service_id_name -> current_name.

Also introduced accessor for current_name into public API to make
current_name read-only..

Renamed internal function get_net_service_name -> get_new_name
NetworkService: removed EnableDisable function

Reasons for removal:
- it worked for netconfig only
- it only Enabled the service
- it was replaced by more generic function EnableDisableNow
Code cleanup
Updated spec
Rspec smoke test for NetworkService
NetworkService: changed API to support more backends (namely wicked)

The change is backward incompatible
Updated changelog
NetworkService: Renamed cur_service_id_name -> current_name.

Also introduced accessor for current_name into public API to make
current_name read-only..

Renamed internal function get_net_service_name -> get_new_name
NetworkService: removed EnableDisable function

Reasons for removal:
- it worked for netconfig only
- it only Enabled the service
- it was replaced by more generic function EnableDisableNow
Code cleanup
Merge branch 'wicked-support' of github.com:mchf/yast-yast2 into wicked-support

Conflicts:
	VERSION
	library/network/src/modules/NetworkService.rb
	package/yast2.changes
	package/yast2.spec
Added helper for checking if a particular network backend is available.
Refactoring NetworkService#Modified
Reduced public API of NetworkService
Merge pull request #116 from mchf/wicked-support

Added Wicked support into NetworkService