Ability to hide/show/delete tabs from tabbedFrame

[jarvisteach]

As mentioned in #332 - should be possible to hide/show/delete tabs from tabbedFrame.

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def deleteTab(frameName, tabName):
    print(tabName)
    tabs = app.widgetManager.get(app.Widgets.TabbedFrame, frameName)

    tab = tabs.widgetStore[tabName][0]
    tab.pack_forget()
    tab.destroy()
    pane = tabs.widgetStore[tabName][1]
    pane.grid_forget()
    pane.destroy()

    del tabs.widgetStore[tabName]

    # to clean up the selected/highlighted tabs
    if tabs.highlightedTab == tabName:
        tabs.highlightedTab = None

    if tabs.selectedTab == tabName:
        tabs.selectedTab = None
        for key in list(tabs.widgetStore.keys()):
            if not tabs.widgetStore[key][0].disabled:
                tabs.changeTab(key)
                break

     tabs._TabbedFrame__colourTabs()