Fixed reveal converter in nbconvert1 to keep stability in the deprecated version

Changes to keep reveal converter live in the deprecated (but useful) version:

* Include missing lexers.py inside nbconvert1/converters/lexers.py 
* Move reveal_base.html from templates inside new nbconvert to nbconvert1/templates/reveal_base.html
* Changes in reveal_base.html to get correct paths to reveal.js folder
* Changes in reveal_base.html to hide social buttons (because I want a basic slideshow and let the user add more features)
* Change reveal.py to get css style from style.min.css

OK, I think it is all... I will get another PR addressing this issues but in the new nbconvert.

Cheers.

Damián.