Fire NProgress on User, Post, and Settings save

Closes #3037
- Created `NProgressSaveMixin`, which extends the `save` method of a model
  to fire NProgress.
- Extended `UserModel`, `PostModel`, and `SettingModel` with the new
  mixin.
- NProgress can be disabled by passing an options hash to the save function with the `{disableNProgress:true}`
- Now that the ValidationEngine isn't the only thing playing with options inside of `model#save`, refactored it to pass the options down the super chain.