ENH: improve cmake/ParaView config handling
Infrastructure for handling user-specfied installation paths for cmake-based code
-prefix=???options and exports them as
CMAKE_INSTALL_PATH, which can be used by cmake.
- the make sentinel file now tracks a variety of parameters (previously just ParaView_DIR and VTK_DIR)
- support plugin builds without predefining a PV_PLUG_PATH environment. Try harder to resolve the paraview-api value if the first attempt fails.
- Unbundle the cmake configuration from the paraview configuration file. Use the
have_cmakewmake/script to access during build only (avoids affecting the PATH).