* Allow exceptions.handle to include user-defined exception types.
    Fixes bug 948536.
  * Adds a wrapper around the form/table header/table in the base
    _data_table.html template for easier targeting/styling.
  * Moves the rest of the main nav templating into a single template
    for easier customization. Fixes bug 948508.

Change-Id: I045c29744ee01f60b080f2c1bbdc79ea5acf1b86