Adding validation when sending only one param to commands

With this change, there will be a unified interface for
sending command params

Before you have to send: '"params":"first_param"'

Now you can send one or multiple params with an array

one param: '"params":["first_param"]'
multiple params: '"params":["first_param", "second_param"]'
Adding params to commands in Web API UI

An input text is added so commands can be called with params.

Right now, you can send params in plain text as if you were calling
a method normally

Example:

def brightness(level)

Command can be called by inserting in input text: 1 and pressing
brightness option in commands button.

If more than one param is sent then use commas to separate them: 1,"2"

This initial implementation is intented only to exercice API by knowing
how you call the commands, expecting a more robust solution later.