Use cascaded deletes

When we delete a user we should delete all the notes that belong to this
user including the revisions of these notes.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

lib/models/revision.js

@@ -102,7 +102,9 @@ module.exports = function (sequelize, DataTypes) {
         Revision.belongsTo(models.Note, {
           foreignKey: 'noteId',
           as: 'note',
-          constraints: false
+          constraints: false,
+          onDelete: 'CASCADE',
+          hooks: true
         })
       },
       getNoteRevisions: function (note, callback) {