Improve deployment: "make deploy"

Why?

Today, deployment is handled by running a custom, platform-specific deployment tool after "make (install)" (if not handled by Qt Creator). There are reasons to unify this under the build system:

• Give all build steps a common, less verbose user interface.
  Before:

  /path/to/qtbase/bin/qmake && make && /path/to/qtbasse/bin/macdeployqt Application.app -qmldir /path/to/app/qml/sources
  

  After:

  /path/to/qtbase/bin/qmake && make deploy
  

• We want the build system to tell us exactly what the application QML files are.
  Today the deployqt tools runs qmlimportscanner in "directiory iteration mode": All qml files in the app source dir is scanned.

Required Changes

• Move deployqt tools to qtbase, as host tools together with moc, rcc. We can then depend on them being present after QtBase is built.
• Introduce QML_SOURCES and use it everywhere, for all application QML files.

Open Questions

• deployqt options: macdeployqt etc has several platform specific options. "make" is not well suited for processing and forwarding command line options.