Added abouthome folder from Firefox's omni.ja.

On my PC, this was located in:

C:\Program Files (x86)\Mozilla Firefox\browser\omni.ja

Within this ZIP file, the abouthome directory was located in:

/chrome/browser/content/browser/abouthome

I also copied the branding directory from /chrome/browser/content/branding
and made it a subdirectory of abouthome.

I also rewrote the URLs in aboutHome.css so they no longer refer to
any chrome: URLs.
point to local abouthome folder instead of chrome: URL.