Refactor a way we setup things on repo controller

Till now, when switching between different views, we were switching
different bindings on repo controller. This was quite innefficient,
because then we needed to add bindings also from other controllers and
it's hard to manage such structure when we would like to add specialized
controllers (like LogController).

The new setup is more declarative, meaning that we do such things on the
router and set things on proper controllers. The only drawback is that
now we need to setup a few observers instead of bindings for "current"
views (ie. when viewing the newest repo or when viewing the last build
in current repo).

At this point it may not look like huge improvement, but it will open a
way to more refactorings.
Rethrow error if the error coming from router is not "Route missing"
Move checking for errors to router rather than template

Previously we were checking if we should display an error message by
adding if statements in a template. This is not the best way to do
it, because it clutters a template and makes code harder to follow.

In this commit I move rendering error templates to the router. Code for
rendering error when there is no builds is not the best way to do it
either, but it can be improved when new router changes are merged to
Ember's master and a way Ember Data is handling promises is revised and
improved.