Rework Conference Page and add Conference Banners

[marcoroth]

The assets/artwork of a conference are part of what sets the vibe of a conference. I would love to be able to convey that "brand" each conference has by adding custom color schemes and conference banners for the conference page, so each conference is special and unique about it.

This could also be a gradual process. For conferences we don't have any assets we might show no banner or some kind of generic banner.

Ideally would collect this for each event:

• Banner image
• Profile Logo Image
• Primary Color
• Secondary Color
• Accent Color