Push new site design to production

This represents several months of work by many dedicated people.
Many thanks to all those who contributed code, issues and fixes!

Amir
Update README.md

use omd >= 0.7.4 (using a lower version may lead to bugs)
update events

temporarily fixes #301 until #234 can be completed
update "edit this page" link to use master branch (instead of redesign)
Add link for IRC
Merge pull request #306 from lpw25/master

Add link for IRC
change tryocaml to html
Add the "alt" attribute to <img> generated by rss2html
Remove the empty "id" from template tryocaml.html

Fixes https://github.com/ocaml/ocaml.org/issues/305
Make the "papers" page respect Markdown syntax.

Fixes https://github.com/ocaml/ocaml.org/issues/307
Fix the tutorial "Introduction to Gtk" so it shows up.
OCamlPro logo: cropped and made transparent
Add a few OCamlPro logos, and update commercial offer description