WIP: HTML presentations using Reveal.js

Different implementation idea in response to pull request #126.

This pull request provides a `MarkdownConverter` implementation that separates the markdown document into multiple slides using the markdown tag `---` (\<hr>) as separator.

The resulting HTML code is then inserted into a specific HTML template for presentations which uses an online version (CDN) of reveal.js to produce the presentation. The presentation is then displayed in the HTML preview:

![reveal_js_preview](https://f.cloud.github.com/assets/603132/2063617/dc53a914-8cb9-11e3-8f7f-4530b56c275d.PNG)

The HTML presentation can be exported using the existing "Export to HTML" menu item.

**This should not be merged yet since there are some rough spots left.**