Update Contributing.md

Fix a typo, add some commas.

Update Contributing.md

Fix link to Template repository.
Add link to Jekyller.

Shower breaks input elements on a page

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

Fixes #132 parsing issue for data-timing

Fix for #99: Inner navigation should be also controlled by slide timing