put contextproperty.h header back

path to this header is hard-coded in lipstick-qt5 unit test :( just no
time to dance around now

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
one more drop to satisfy hard-coders

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
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Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>