The stacked opendev logo is added to the home page as an svg.
A 120x120 ping is added as the gitea icon. It appears in several
places throughout gitea source code, and therefore it's easier to
just replace it using the same filename and format rather than
updating the templates with a new filename.
Change-Id: I888b8913c7b6a1045975f10240d744d09b9355b0
b228fec4c6