initial trial to custom header for sub-sites

Created by: flora8984461

Fix #88 (closed)

One example can be https://deploy-preview-196--eclipsefdn-hugo-solstice-theme.netlify.app/subsite-1/ You can assume it is a subsite with its independent logo and logo url.

Another example can be https://deploy-preview-196--eclipsefdn-hugo-solstice-theme.netlify.app/third-parent/ You can assume it's another subsite with another independent logo and logo url.

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