Implement Dirty forms component with Turbolinks and custom event support

[danguita]

Connects to #240.

What does this PR do?

This PR implements a JS component which will be responsible for warning for unsaved changes when leaving a page. It is supporting Turbolinks and implements custom events that can be triggered by other UI components.

This behavior can be skipped by adding the .skip-dirty-check class at form tag level.

How should this be manually tested?

We would need to check that changes are detected and the alert dialogs are shown as expected:

• Detects changes any kind of form input controls (<input>, <select>, <textarea>).
• Detects text changes in a WYSIWYG control (Trix).
• Detects file attachments in a WYSIWYG control (Trix).
• Detects changes in a date picker control.
• It can intercept a Turbolinks event, or leave it to the beforeunload window event.
• The confirm/alert dialogs are displayed when forms are dirty 🙌

Confirm dialog triggered while listening to Turbolinks events:

Native beforeunload event dialogs (leave and reload):

[ferblape]

Works really well!