Remove NOT NULL constraints on globalized fields

It seems that the Rails 4.2-compatible version of Globalize does not
play well with NOT NULL constraints on the globalized attributes. Remove
the constraints to work around this issue.

db/migrate/20150408204739_remove_not_null_constraint_on_conference_title.rb

@@ -0,0 +1,5 @@
+class RemoveNotNullConstraintOnConferenceTitle < ActiveRecord::Migration
+  def change
+    change_column :conferences, :title, :string, null: true
+  end
+end

db/migrate/20150408204855_remove_not_null_constraint_on_conference_description.rb

@@ -0,0 +1,5 @@
+class RemoveNotNullConstraintOnConferenceDescription < ActiveRecord::Migration
+  def change
+    change_column :conferences, :description, :text, null: true
+  end
+end

db/migrate/20150408205015_remove_not_null_constraint_on_track_name.rb

@@ -0,0 +1,5 @@
+class RemoveNotNullConstraintOnTrackName < ActiveRecord::Migration
+  def change
+    change_column :tracks, :name, :text, null: true
+  end
+end