cmake: Add msbuild integration to the install

This adds the msbuild integration files to the install, provides batch scripts
for (un)installing it in a convenient way, and hooks up the nsis installer to
run those scripts.

Differential Revision: http://llvm-reviews.chandlerc.com/D1537

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189434 91177308-0d34-0410-b5e6-96231b3b80d8