* Print background in pdf

Pull request to integrate issue https://github.com/hakimel/reveal.js/issues/1686. Adding the workaround to the theme template to make it work for every theme.

* apply suggestion of @hakimel

Prefer W3C pointer events and updates to match the standard definition

Updates copyright to 2018

* add support for overriding the default layout
New `overrideLayout` option (if true) will prevent h/w calcs.

* fix error if options are empty

* Implement requested changes
Rename overrideLayout to disableLayout and remove code to unset display

This reverts commit f76b4fda.

Prefer W3C pointer events, remove pointerEnabled references (it is not part of the standard), unconditional event removal

Allow whitespace on background-images, w3 compliance

This prevents additional requests from devtools when debugging code.

Closes #2005.

Closes #2075.

Closes #1951.

Closes #1808.

Windows carriage return line endings were not being tested for.

Fixes #2087.

Update dependencies.

Allow `data-background` images to load even if there is whitespace at…