Enable 'plpgsql' PG extension during conversion

[jacobvosmaer]

This is a difference between 'converted' PG databases and 'original' PG databases.

diff --git a/db/schema.rb b/db/schema.rb
index 04abf9b..9da616f 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -13,9 +13,6 @@

 ActiveRecord::Schema.define(version: 20150502064022) do

-  # These are extensions that must be enabled in order to support this database
-  enable_extension "plpgsql"
-
   create_table "application_settings", force: true do |t|
     t.integer  "default_projects_limit"

We should probably just enable the extension during the import.

cc @DouweM @dosire