fix: consolidate some duplicated code

i feel like there was a reason i hadn't done that to begin with, but
now can't recall for sure.  pylint certainly thinks it is duplicated
so mostly cleaning this up per its suggestion...

docs/api/sideshow.web.util.rst

@@ -0,0 +1,6 @@
+
+``sideshow.web.util``
+=====================
+
+.. automodule:: sideshow.web.util
+   :members:

docs/index.rst

@@ -59,6 +59,7 @@ For an online demo see https://demo.wuttaproject.org/
    api/sideshow.web.forms.schema
    api/sideshow.web.menus
    api/sideshow.web.static
+   api/sideshow.web.util
    api/sideshow.web.views
    api/sideshow.web.views.batch
    api/sideshow.web.views.batch.neworder