Add initial implementation of YAML config file

This implements the basic framework that allows global YAML
configuration, per-environment custom configuration, and unit-
test-specific configuration.

TESTED=I deployed to alpha, ran some EPP commands through the
nomulus tool, and verified no errors.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=145422680

java/google/registry/env/sandbox/common/WEB-INF/nomulus-config.yaml

@@ -1,10 +1 @@
-
-appEngine:
-  projectId: domain-registry-sandbox
-
-registryPolicy:
-  contactAndHostRoidSuffix: GOOGLE
-  productName: Google Registry Sandbox
-
-registrarConsole:
-  logoFilename: google_registry.png
+# Add environment-specific configuration here