Fix critial bug in text itemizer.

Itemizations is invalid after changing text, therefore lists have to be cleared.
Implement upright=right_only/left_only.
Closes #1533.
Show missing glyphs by rendering boxes instead of dropping the whole text.
Force strict mode for loading test maps.
Font directory.
Add missing reference images.
Update reference images for scale_factor 2.0.
Remove broken images for test "simple.xml" rendered with cairo.