'Add a toolitem to the container
This method must get implemented per backend
The callback associated with the button click event,
must be **EXACTLY** `self.trigger_tool(name)`
Parameters
name : string
Name of the tool to add, this gets used as the tool\'s ID and as the
default label of the buttons
group : String
Name of the group that this tool belongs to
position : Int
Position of the tool within its group, if -1 it goes at the End
image_file : String
Filename of the image for the button or `None`
description : String
Description of the tool, used for the tooltips
toggle : Bool
* `True` : The button is a toggle (change the pressed/unpressed
state between consecutive clicks)
* `False` : The button is a normal button (returns to unpressed
state after release)'

def add_toolitem(self, name, group, position, image, description, toggle):

    raise NotImplementedError
