win: support for Visual Studio 2017

win: support for Visual Studio 2017

This patch enables building openvpn with Visual Studio 2017.

It is advised to use openvpn-build/msvs/build.bat which
also downloads and build required dependencies.

Changes made:

 - updated path to Visual Studio toolchain
 - updated platform toolset
 - added missing libraries
 - added x64 configurations
 - enabled AEAD ciphers to make NCP work
 - enabled unicode support
 - updated source files in project settings
 - fix includes
 - restored variable which was erroneously removed
 - added properties file which sets required env variables
 	(required to build with IDE)
 - etc

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Simon Rozman <simon@rozman.si>
Message-Id: <1538141209-32330-1-git-send-email-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17499.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>