added StyleCop.MSBuild to all projects

I can see from the history that StyleCop analysis was added to the build script at one point but then reverted. This PR shows how it can be done with StyleCop.MSBuild and configured to make it an unobtrusive way to get StyleCop running with every single build whilst placing no additional burden on contributors or coordinators.

Things to note:

* all rules which are currently violated are switched off in Settings.StyleCop so no warnings are currently being generated in the build output
* all rules which are currently complied with are switched on in Settings.StyleCop
* any future violations will only be reported as warnings rather than errors so will not affect build success
* StyleCop analysis is very fast and does not noticeably affect build time (unlike FxCop)
* edit-stylecop-settings.cmd is added as a convenient shortcut for editing Settings.StyleCop in StyleCopSettingsEditor.exe (also contained in the NuGet package)
* later, if/when it is desirable and/or convenient, rules can be switched on one by one using StyleCopSettingsEditor.exe and addressed appropriately

Things to note about the StyleCop.MSBuild package as opposed to other methods of StyleCop invocation:

* runs on *every* build, whether in VS, from command line, on local machine, on build server, etc.
* fully compatible with NuGet package restore since NuGet 2.7
* self contained package which does not rely on a StyleCop installation on any machine