Add UI to discover translated SVG files.

Currently we support rendering SVGs in multiple languages,
but there is no mechanism for users to discover what languages
a file is available in. Show this information on the image page.

At the moment, if unspecified we always default the language to
english (I believe to avoid mass cache splitting, especially
if most languages wouldn't have a translation of the file in
their language). This code was written in such a way so that
this assumption should be changable in the future if we so
desire.

Long term, Jarry has a super cool svg translation extension
which would take over some of this. However I still believe
we should have an interface for this in core, since we do
support the different language renderings in core.

Change-Id: I84506436514e09d71200aa2db3932aa001b55c71
Merge "Add UI to discover translated SVG files."