Plugin: Fix "Keep" bug

Ensure that "Keep" always uses the start of the current selection to
determine the conflict it should work with.
Docu: Fix spelling errors and duplicate words
Docu: Add message for 1.4.3
Plugin: Fix "Keep" bug

 - Ensure that "Keep" always starts its search for a conflict at the
   beginning of the current selection
 - Fix various spelling and duplicate words errors in the documentation