INTEGRATE: v0.6 documentation updates

* dev:
  PositionDescriptor documentation tweaks
  Descriptor overview tweaks
  Revert object name with descriptor properties
  Descriptor docs include object name with properties
  Descriptors documentation tweak
  QElement documentation tweaks
  QFrame.resize() documentation tweak
  QFrame.getAll() documentation link fix
  QFrame.reset(), remove() documentation improvements
  quixote module documentation improvements
  Readme tweak
  API overview tweaks
  API overview documentation updates
  QElement documentation no longer includes descriptors
  Changelog updates for 0.6 release
  Roadmap updates for 0.6 release
  Better documentation cross-linking
  Descriptor tutorial tweaks
  QViewport.md and QPage.md docs subsumed into descriptors.md
  Size descriptor documentation is in SizeDescriptor.md
  Position descriptor documentation is in PositionDescriptor.md
  All descriptor properties listed in descriptors.md
  Outline for 0.6 API doc updates
  Roadmap updates