XOS/NEM charts, use a global registry var, split docker image name/tag/pullPolicy

Change-Id: I7f3457882830de050d1357254fc5483faf91d03f
diff --git a/xos-db/values.yaml b/xos-db/values.yaml
index 8bb026d..8428769 100644
--- a/xos-db/values.yaml
+++ b/xos-db/values.yaml
@@ -15,8 +15,13 @@
 
 # XOS Postgres database related values
 
-imagePullPolicy: 'Always'
-postgresImage: 'postgres:10.3-alpine'
+image:
+  repository: 'postgres'
+  tag: '{{ .Chart.AppVersion }}'
+  pullPolicy: 'Always'
+
+global:
+  registry: ""
 
 # Database name/username/password
 xosDBName: 'xos'