BUG: Ensure header files appear in IDE project files

Add custom targets where appropriate in CMakeLists.txt to ensure that *.h and
*.txx files appear in project files for MSVC, Xcode, etc. If a static library
is already being built, simply add header files to that target.

Change-Id: I19ce5c9ce002119238b485a65eb73f65f679c265
Merge topic 'CMakeShowHeadersInIDEs'

5153fe4 BUG: Ensure header files appear in IDE project files