feat: add Sponsors section

[toshi835]

Note

changes are

• add PC chairs members in organizers page
• add e-mail address of PC chairs in organizers page
• add sponsor section in home
• add one silver sponsor

After this code change, page would become followings

• home page

• organizer page

Future Image

Also tested future home page after getting more sponsors

[toshi835]

@takatoy please update CSS or visual if needed as I am not good at it haha