Calls ButtonClick method.
procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X: Integer; Y: Integer); override;
Determines button at cursor and calls ButtonClick method.
The Button parameter determines which mouse button the user pressed.
Shift indicates which shift keys (Shift, Ctrl, or Alt) were down when the user pressed the mouse button.
X and Y are the pixel coordinates of the mouse pointer within the client area of the TCustomBtnPanel.