Basic scenegraph inspection features.

Very basic, currently static, with some not working code for automatic
refresh of the tree, some stupid dead code and many stupid printfs.
Refresh scenegraph dynamically.
Synchronize item and scenegraph selection.
Increment protocol version.
Fix double occurrence of childCount.
Reset property viewer when deleting current node.

This prevents a crash due to trying to access a getter of an already
deleted node.
Auto-expand sgTreeView & auto-resize object column
Compile with Qt 5.1.
Move the private include directory to the plugin that needs it.
Decouple the QSG inspector from HAVE_PRIVATE_QT_HEADERS.

It only works out of the box with Qt 5.2.0 due to the need for private V8
headers which we don't get readily filled CMake variables for.
Make this also work with Qt4.
Check if the server provides the property controller at all.

This is a workaround for crashes with servers that don't provide the QSG
tree, we still need to properly hide the QSG UI in this case.