usermanual: update on highlight reconstruction
Updated Czech translation
Add support for rotating the wattermark.
Minor reformatting.
Merge branch 'rotate-watermarks'

* rotate-watermarks:
  Minor reformatting.
  Add support for rotating the wattermark.
Update French translation.
Merge pull request #589 from milankni/translation-cz

Updated Czech translation
Fix watermark rotation direction.
Add "screen_dpi_overwrite" to config

Setting this to a value > 0.0 will overwrite the screen's DPI setting to
scale the GUI accordingly without the need to mess with xrandr.
Fix computation of watermark center.