UI: Separated checkbox for IPv6 enablement.

All references to old forwarding flag were renamed to forward_v4. E.g.
RoutingClass::Forward -> RoutingClass::Forward_v4 and similarly in other
cases.

Also some cleanup work is present. Mainly removing blank lines.
Added backend for separated IPv6 enablement and some cleanup. bnc#572202

Cleanup is related to YCP -> Ruby conversion.
Minor update in old testsuite to keep things working.
Created new spec for Routing.
Removed dead code from services/routing.rb
Removed some artifacts from YCP->Ruby conversion from services/routing.rb
Extended new tests for routing.

Added more tests on Routing#WriteIPForward.
It covers tests from old testsuite now.
Style guide adoptions