* Admins can manage the working plan of a single provider on the backend/users page.
* Before sending a new notification email the system checks whether the provider user has notifications enabled.
* Added salt field in the "ea_user_settings" table.
* 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.
