cube: Use VK_KHR_incremental_present extension

Show how to use the VK_KHR_incremental_present extension.  Other notes:

- There are a few diagnostic DbgMsg()'s, which can help show the usage.
- Added a "--incremental_present" command-line option to turn on use of
  VK_KHR_incremental_present
- Should compile and run on Windows, Linux, and Android, but the feature will
  only really be used on systems that support the extension.