Added backend API for stats

pkg/models/stats.go

@@ -18,3 +18,18 @@ type GetSystemStatsQuery struct {
 type GetDataSourceStatsQuery struct {
 	Result []*DataSourceStats
 }
+
+type AdminStats struct {
+  UserCount       int
+  OrgCount        int
+  DashboardCount  int 
+  DBSnapshotCount int
+  DBTagCount      int
+  DataSourceCount int
+  PlaylistCount   int
+  StarredDBCount  int
+}
+
+type GetAdminStatsQuery struct {
+  Result *AdminStats
+}