Logo is not hosted on Apache site

[hen]

The logo doesn't display for me (because I block cross-site calls). This is because it's coming from the old mxnet.io website. We should move that file over to this GitHub.

[lupesko]

+1
The logo update is being discussed in the community - once we have a final decision we can make the change for the new logo.

[lupesko]

+1 again.
There's 4 images that are loaded off dmlc/web-data instead of being loaded off apache/incubator-mxnet:

• mxnet_logo.png
• apache_incubator_logo.png
• mxnet-background.png
• mxnet-navbar.png

We need to have all of them hosted on the Apache website.
Tagging @thinksanky