Add version to About dialog

gitversion.cmake

@@ -0,0 +1,19 @@
+set(_build_version "unknown")
+
+find_package(Git)
+if(GIT_FOUND)
+  execute_process(
+    COMMAND ${GIT_EXECUTABLE} describe --tags HEAD
+    WORKING_DIRECTORY "${local_dir}"
+    OUTPUT_VARIABLE _build_version
+    ERROR_QUIET
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+  message(STATUS "GIT hash: ${_build_version}")
+else()
+  message(STATUS "GIT not found")
+endif()
+
+message(STATUS "local:${local_dir} output:${output_dir}")
+
+configure_file("${local_dir}/gitversion.h.in" "${output_dir}/gitversion.h" @ONLY)