Make the tablet tester dialogue translatable

For the non-mouse events, special care had to be taken
to avoid ‘word puzzles’. The translator can specify
how the device and action strings should be combined,
so that, e.g., the two strings ‘Stylus’ + ‘release’,
which are combinted into ‘Stylus release:’ in English,
can have a different word order in the translation,
e.g. ‘Release of Stylus:’ or ‘Stylus – release:’.