[Enhancement] Improve flow for adding many sources at once (#306)

* Added mechamism for using existing sources as a reference for adding new sources

* Added test

lib/pinchflat_web/controllers/sources/source_controller.ex

@@ -41,13 +41,30 @@ defmodule PinchflatWeb.Sources.SourceController do
     render(conn, :index, sources: Repo.all(source_query))
   end
 
-  def new(conn, _params) do
-    changeset = Sources.change_source(%Source{})
+  def new(conn, params) do
+    # This lets me preload the settings from another source for more efficient creation
+    cs_struct =
+      case to_string(params["template_id"]) do
+        "" -> %Source{}
+        template_id -> Repo.get(Source, template_id) || %Source{}
+      end
 
     render(conn, :new,
-      changeset: changeset,
       media_profiles: media_profiles(),
-      layout: get_onboarding_layout()
+      layout: get_onboarding_layout(),
+      # Most of these don't actually _need_ to be nullified at this point,
+      # but if I don't do it now I know it'll bite me
+      changeset:
+        Sources.change_source(%Source{
+          cs_struct
+          | id: nil,
+            uuid: nil,
+            custom_name: nil,
+            collection_name: nil,
+            collection_id: nil,
+            collection_type: nil,
+            original_url: nil
+        })
     )
   end