qmljs: added qmljsconstants.h

Moved Document::Language, Import::Type and StaticAnalysis::Severity
enums to qmljsconstants.h and renamed values removing the redundant
part.
Thus the effective length changed little or improved
(Document::QmlLanguage => Language::Qml).

The separate file allows better reuse of enum values without introducing
circular dependencies.

Change-Id: I5186d7c04f5d3f6c289068b919be5ff1ff118326
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
qmljs: simple tracking of used modules

Change-Id: Idc977a8c5a6c6caa3749599cb6f4a236046f53d7
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>