Display exercises available for nitpick in language track order #1720
Merge pull request #2108 from code-R/2091-nitpick-exercises-in-language-track-order

2091 nitpick exercises in language track order
Extend custom alert classes with bootstrap styling

This allows custom alert classes such as:
  .alert-notice
  .alert-error
  .alert-alert

To be styled by bootstrap as though we were using the standard classes:
  .alert-info
  .alert-danger
  .alert-warning