gitweb: Link (HEAD) tree for each project from projects list

gitweb: Link (HEAD) tree for each project from projects list

Current projects list is oriented on easily getting "what's new"
information. But when already using gitweb as an interface to something,
I personally find myself to _much_ more frequently wanting to rather
see "what's in" (or "what's new in") and it's quite annoying to have to
go through the summary page (which is also rather expensive to generate)
just to get there.

Signed-off-by: Petr Baudis <redacted>
Signed-off-by: Junio C Hamano <redacted>