Introduce new USE_QT4 component linguisttools for lrelease/lupdate tools
split from from devel/qt4-linguist (similar to Qt 5 ports). These console
tools are often used for localization support in Qt ports, having them
standalone is quite useful. This work is based on Tobias Berner patch [1].
PR: 190929 [1]
Requested by: amdmi3, koobs