Update cube sample to modern conventions, imgui, tg

3 jobs for feature/high-dpi in 18 minutes and 12 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed clang-buster #81604
Linux buster

00:16:42

passed gcc-buster #81603
Linux buster

00:01:30

passed VS2017-x64 #81602
VS2017

00:04:08