[cmake-developers] Add more options for NSIS installer artwork

Hi cmake-developers, (first of all, this is my first patch submission, so guidance is appreciated, thanks). I sent a similar patch as plain text in an email to the list last Friday, but after observing the email traffic It looks like you prefer attachments. I also added documentation to this

[cmake-developers] [PATCH] add options to set the bitmap for NSIS installer left side

>From 5cd81e17a51c5dc74e494c39a5f496f8e54a5bbf Mon Sep 17 00:00:00 2001 From: Colin Tracey Date: Fri, 25 Sep 2015 15:06:08 -0500 Subject: [PATCH] add options to set the bitmap for NSIS installer left side set MUI_WELCOMEFINISHPAGE_BITMAP set MUI_UNWELCOMEFINISHPAGE_BITMAP --- Modu