coding style and variable naming

[andy-Chien]

The action name Hiwinmodbus is vague and confusing. For the user, that action is not associated with modbus.
IP address should be passed in by parameter system, not via action goal.
Automatically connect to the robot when launch this node should be better.
Name of class member variables should start or end with underscore, and they are usually private.
The declaration of member variables in a class is usually placed after functions.

[andy-Chien]

@errrr0501 ☝️

[errrr0501]

@andy-Chien after failed on sending command with action, I have try with service, and it worked well, the reason that action couldn't worked probably was because of muti-thread(every time action client call action server), yet not sure about that, also, I think there's no necessary to use action on modbus transport, so I change to service, could you please check those variables naming or coding style when you have time .

[errrr0501]

P.S. sorry for forgetting Link Commits, will link with next push.