Save device logs to rethinkdb.

lib/db/tables.js

@@ -5,4 +5,11 @@ module.exports = {
 , devices: {
     primaryKey: 'serial'
   }
+, logs: {
+    primaryKey: 'id'
+  , indexes: {
+      serial: null
+    , timestamp: null
+    }
+  }
 }