Move exports conflicting with QtDeclarative into namespace

Move exported qml* symbols that conflict with QtDeclarative into an
- automatically imported - namespace. This ensures apps can
link against both QtDeclarative and QtQml.

To keep the BC promise the old symbols are still exported.

Task-number: QTBUG-29584
Change-Id: I3d31c36ca4e2faaf6f5d67a77c5c5a304c0338a4
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>