Whenever a build starts other builds from its downstream builds, the user
should be able to see a tree of those builds. Right now it's possible to check
the builds by going through all the builds and the corresponding links, but
it's slow and error-prone.

So, a new view should exist which shows the root build and all of its
downstream builds and their downstream builds etc. regardless of whether they
already have been built or are going to be in the queue. Every build should
have a link which leads the the build's page and its build number.
To make it easier to implement, the view could be just an indented list instead
of a graphical tree, like

A build 37
B build 33
C build 78
F build 142
T build 71
G build 91