Visual Studio 2017 preview

Added fake support for VS 2017 in the addin xml. Visual Studio 2017 still complains when installing these extensions, but if you ignore it they should still come online after installing.

Visual Studio 2015

This is the first version with Visual Studio 2015 support. Moved over to vsix packages.

NiftyPlugins 1.6.0

Small fix for HiDPI monitors.
Moved the build system over to Win10 + VS2013.