Add function to apply context menu to widget

[UnsignedArduino]

If we add a context menu to a widget that already has on "built-in" (like entries, text, etc.) then it will add it under. Maybe something like this:

def make_menu_for_widget():
    # return a TkZero menu object that has all the commands and everything set to their respective states
    # if nothing is returned then don't show a context menu
    # this function will be called everytime before we show the right-click menu

add_context_menu(widget, make_menu_func=make_menu_for_widget)

[UnsignedArduino]

Actually, we should never put on a context menu by default, and have a built in function that will return a "standard" right-click menu for typing widgets (like "cut" "copy" and "paste) for widgets.
Maybe an API like this:

from TkZero.Menu import add_context_menu, entry_context_menu, ContextMenu

...

def make_menu_for_widget():
    # return a TkZero menu object that has all the commands and everything set to their respective states
    # if nothing is returned then don't show a context menu
    # this function will be called every time before we show the right-click menu
    menu = ContextMenu(parent)
    # this will add items before and after a "standard" context menu
    menu.items = [(the menu objects we already have, like MenuCommand)] + entry_context_menu(entry) + [(more menu objects)]
    return menu

...

add_context_menu(entry, make_menu_func=make_menu_for_widget)