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.
I was wondering about this. Are we going to convert options classes to auto before auto has builder patterns? From a user prospective I would imagine it is nice to work with builders.