ICU-13586 No actual code changes. This change cleans up redundancies in the VS projec...

ICU-13586 No actual code changes. This change cleans up redundancies in the VS project files, and pulls in common or shared settings from a shared 'props' file. This means that you can now change one single file to target either VS2015 or VS2017, instead of needing to change many files. It also allows the VS project files to share common defines as well, meaning that if you need to target something other than Windows 7, you can make one change in one file, instead of needing to make hundreds. Also included in this change are improvements to the VS Solution files in order to properly denote the dependencies of the projects, which might be needed in the future for possible parallel project builds.

X-SVN-Rev: 41049