Replace package dependency list with package loading queue.

It's more comfortable to use on the client-side. Loading queues contain
names of _all_ the packages are needed to load.
Add support of nested package dependences on the client-side.
Fix stylesheets loading on pages.
Implementa non-initial dependency loading on the client-side.
Fix initial dependency loading on the client-side.

Mark stylesheets as loaded for all of the initial dependences.