* Fix the validation for some "input[type=number]" element;
  By default, the number type input only accept *integer*. By setting
  the 'step="any"' attribute, the float numbers are also valid.
* Add form input validation styles for ":valid" and ":invalid" pseudo
  classes.

* Rewrite "configs.js" to be more modular and generic
* Bind functions to button click event
* Implement the function to set form fields to given configuration data
* Implement the function to reset server-side configurations
* Implement the function to load user configuration file on server
* Implement get the configuration data from the server