Do not hijack hjkl/home/end keys when in list mode.

This makes it possible to use forms on pages which load shower.js
and do not contain a presentation, and to use forms on a page
that are unrelated to a presentation and no presentation is being
shown.

Fixes #141
Merge pull request #141 from Patternslib/issue-141-key-hijack

Shower breaks input elements on a page