msvc: Move common project settings to reusable property sheets

msvc: Move common project settings to reusable property sheets

The Visual Studio 2017 project files were refactored by migrating all
repeating common settings into three property sheets: Debug.props,
Release.props and the existing PropertySheet.props.
This simplifies configuration management while providing uniformity
across projects, configurations and platforms.
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20181008094600.10164-2-simon@rozman.si>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17634.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>