Fix strings containing deprecated illegal escape sequences (#648)

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.

windows/nonAIO/builder/build_GrampsWin32.py

@@ -222,7 +222,7 @@ class buildbase(GObject.GObject):
             os.makedirs(mo_dir)
         #TODO: find a better way to handle  different platforms
         if sys.platform == 'win32':
-            po_files = glob.glob(po_dir + "\*.po")
+            po_files = glob.glob(po_dir + r"\*.po")
             # no longer using python msgfmt as it doesn't handle plurals (april 2010)
             # msgfmtCmd = path.normpath(path.join(sys.prefix, "Tools/i18n/msgfmt.py") )