Order layer outputs in the order they were added (#1399)

Summarize your change.
When adding multiple outputs to a layer, they are not returned in the same order as they were added.
This adds a new SERIAL column which auto-increments to the layer_output table.

With the correct order, it's possible to determine the "main" output of a layer by using the order.

VERSION.in

@@ -1 +1 @@
-0.29
+0.30

cuebot/src/main/java/com/imageworks/spcue/dao/postgres/LayerDaoJdbc.java

@@ -77,7 +77,9 @@ public void insertLayerOutput(LayerInterface layer, String filespec) {
         "FROM " +
             "layer_output " +
         "WHERE " +
-            "pk_layer = ?";
+            "pk_layer = ?" +
+        "ORDER BY " +
+            "ser_order";
 
     private static final RowMapper<String> OUTPUT_MAPPER =
         new RowMapper<String>() {

cuebot/src/main/resources/conf/ddl/postgres/migrations/V30__Add_order_column_to_outputs.sql

@@ -0,0 +1,3 @@
+-- Add a serial column to layer_output for getting correct order of outputs
+
+alter table layer_output add ser_order SERIAL not null;