Add scoring engines to database and API layers

A Scoring Module needs to expose a list of available
scoring engines through API and Watcher CLI. This list
is stored in database and synchronized by Decision Engine.

Partially-Implements: blueprint scoring-module
Change-Id: I32168adeaf34fd12a731204c5b58fe68434ad087
APIImpact

etc/watcher/policy.json

@@ -31,6 +31,10 @@
     "goal:get": "rule:default",
     "goal:get_all": "rule:default",
 
+    "scoring_engine:detail": "rule:default",
+    "scoring_engine:get": "rule:default",
+    "scoring_engine:get_all": "rule:default",
+
     "strategy:detail": "rule:default",
     "strategy:get": "rule:default",
     "strategy:get_all": "rule:default"