feature/Pages for Each SIG

[SalihSaygi]

To filter out the events into their SIGs, I think it is a good idea to have pages for each SIG and their description, SIG leaders related to it with their contact information, and events (filtered into past, future, and new sections).

This might not be necessary as we don't have many SIGs active right now so, I think this is an idea that could be done if there are more SIGs active.