Update Glade support + fix bugs encountered along the way

• List HdyAvatar
• List HdyKeypad
  • Filed #251
• List HdyViewSwitcherTitle
  • There are some breaking bugs, but that's preexisting problems from HdyViewSwitcher Nevermind, it actually works :p
• List HdyDeck
  • Can't add children to it properly, but that's a preexisting problem with leaflet
• List HdyWindowHandle
• List HdyWindow
  • This one required some glue code to be able to add children properly...
  • ...and a dtd update
  • Noticed and fixed a bug with show_all()
  • Noticed that we allowed to add >1 children. Fixed
  • Noticed that we included the HdyNothing into foreach(). Fixed
  • This triggered #244 (closed) badly, fixed
• List HdyApplicationWindow, see HdyWindow
• Re-sort HdyCarousel, it wasn't moved during the rename