* Fixed minor issues with backend.
* Fixed get_provider_available_time_periods() method - now works correctly.
* Added unavailable notes in the calendar (under the "Unavailable" title).
* Updated the thesis code snippets.
* Added listings.pdf, a free ebook about latex listings.
* Regenerated code docs (js + php).
* Added custom error 404 page.
* Added service price and description in the appointment booking wizard.
* Completed Issue #21 - devide services in categories in the appointment booking wizard.
* Completed the backend user management page.