Adapted the event handler that marks entries as read via AJAX to Bootstrap 3.

This event handler had stopped working because the event name has changed in Bootstrap 3. Instead of "show" now it's "shown.bs.collapse".
Use a darker bg-color when hovering over folders and unread entries.

The older color scheme was not different enough between non-hover and hover states.
Folders in the sidebar no longer have a margin between each other.
Simplified Simple_form initialization.

We only use one simple_form wrapper in all the app, which is supposed to generate markup compatible with bootstrap forms with prepended icons (even though it's not currently working because of the migration to Bootstrap 3). Removed from the app initializers all other wrapper definitions, which were unused clutter. Also set the only wrapper as the default one, so that each form does not have to explicitly declare which wrapper to use.
Simple_form adds class "form-horizontal" to forms by default.

This removes the need to explicitly declare it in each form.

Also the "btn btn-default" classes are used by default for buttons, instead of just "btn". This is necessary because buttons in Bootstrap 3 no longer have styling unless given the "btn-default" or alternative class.

Also enabled browser-side validations by default.
Added bootstrap 3 grid classes for controlling the width of form elements to the default simple_form config.

Also changed simple_form configuration to use the ruby 1.9 hash syntax.
Use the github repo as source for Simple_form gem.

We need support for the config.input_class option in simple_form. This has been added in the last 15 days and is not yet present in any tagged version. As soon as a tagged version or, even better, a stable release has this support, we will switch back to using a released gem or tag.

This is necessary to add "form-control" class to all inputs in forms, which is a requisite for Bootstrap 3 compatibility.

For more details about integration between simple_form and bootstrap 3 see:

    http://stabco.tumblr.com/post/59760641051/simple-form-bootstrap3-integration
Adapted styles used by simple_form wrapper and input generators to be compatible with Bootstrap 3.

Prepended icons now work correctly.