Python 3.6 and above has deprecated illegal string escape sequences. Escape sequences are preceded by a '\' and valid ones are "\n\t\r" etc. Illegal ones are not in the list https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals.
Previous to Python 3.6 these illegal sequences were ignored and the '\' was left in place. Pylint has been noting these for a while now.
This PR corrects these sequences in Gramps. I used
find . -name "*.py" | xargs -t -n 1 python3 -Wd -m py_compile 2>&1 | grep Depre
to locate the failing strings.
