Add mousewheel event listener

Don't call iterate DOM several times in event handlers

Fugbix typo

Fix the getCurrentSlideNumber to return 0 when it fails to find a slide

add .editorconfig feature

Clear the console only in slide mode, fixes #125

Key handling refactoring

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