Modify Qt for MCUs template to place all qmlproject sources inside qmlproject subdirectory

To simplify the user's integration of Qt for MCUs into their own projects, we place all the qmlproject related files in a subdirectory under the project directory (which is probably otherwise empty)

Target project template structure:

• Root                                // name of the project configured in the new project wizard
  • qmlproject           //  contains everything from the current project template
    • <all qml and asset files>
    • <project_name>.qmlproject
    • CMakeLists.txt
  • CMakeLists.txt