Called when user presses the 'send' button or presses 'Enter' while the command entry box has focus.

def onSendCommand(self):
        '''Called when user presses the 'send' button or presses 'Enter' while the command entry box has focus.'''
        self.agent_host.sendCommand(self.command_entry.get())
        self.command_entry.delete(0,END)
        self.canvas.focus_set()