Renaming root files to index.html for cleaner urls

Instead of having a link to lectures/lectures or rooftop/rooftop,
web servers will search for a default page in every folder (index.html).
By having an index, the URL would be http://spiritsenthusiastsociety.com/lectures/
instead of http://spiritsenthusiastsociety.com/lectures/lectures.html etc
A bunch of style changes and some code reorganization