qdistancefieldgenerator: Properly install tool

Also rename executable to qdistancefieldgenerator

Change-Id: I2951c2d83fcff25d65413a548f7a692980c9b3ec
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/distancefieldgenerator/distancefieldgenerator.pro

+TARGET = qdistancefieldgenerator
+
 QT += gui widgets gui-private core-private quick-private
 
 SOURCES += \
@@ -18,3 +20,7 @@ HEADERS += \
     distancefieldmodelworker.h
 
 QMAKE_DOCS = $$PWD/doc/qtdistancefieldgenerator.qdocconf
+
+QMAKE_TARGET_DESCRIPTION = "Qt Distance Field Generator"
+
+load(qt_app)