L7 rebased

Adds coverage of the TargetHttpProxyApi, UrlMapApi, GlobalForwardingRuleApi, and BackendServiceApi.

Also adds a complete License file to the top level.

I apologize for the large size of this PR.
Ex.

InputType.builder().rules(rules).name(name).build() // build calls
auto factory method (one with SerializedNames)

as this is very likely to match what auto will do in the future.