In several cases we don't want menu(s) to close when an action on menu was
done. For example on drag-n-drop or menu item deletion (where confirmation
dialog is shown).
In such situations `s_bPreventClosing` was set to true (and then back to
false when closing was allowed again).
Though original code honored this variable only in certain situations and
typically (at least on Win10) menus were hidden/closed despite of it.
This patch changes the behavior and menus(s) are not closed when
`s_bPreventClosing` is set to true.
Basically now menu(s) stay visible until there is an action that changes
active window.
Following functionality was also removed because it is not needed now:
* CMenuContainer::HideTemp
* COwnerWindow::OnClear
WM_CLEAR was sent to the window only by already removed `HideTemp`
* Fix naming inconsistencies
'Menu' vs 'StartMenu'
* Installer: Remove Facebook link
* Installer: Remove PayPal donate remnants
* OpenShellReadme: Remove info about product version
