Update Logo and banner bg

Created by: flora8984461

According to https://github.com/EclipseFdn/osgi.org/issues/3#issuecomment-782190103

But this banner bg is a little bit less accessible, wdyt?

And this is the smallest I can compress to. Unless I change the size. Let me ask @meKokabi .

Signed-off-by: Yi Liu yi.liu@eclipse-foundation.org