Try to import escape from html module

I got a deprecation warning: wtforms/widgets/core.py:45: DeprecationWarning: cgi.escape is deprecated, use html.escape instead

I investigated, and found that cgi.escape is deprecated since 3.2 (I'm using 3.4):
https://docs.python.org/3.4/library/cgi.html#cgi.escape

Crucially, html.escape has quote=True by default and cgi.escape has quote=False by default. I have changed the escape calls so that they all explicitly set quote=True or False, so functionality should be unchanged. (There is another call in the file that already sets quote=True.) I'm unsure as to whether the places where quote=False actually want to be changed, but I thought that should be a separate pull request, if needed.