collect_dir() will now pre-load all files and return a function that will
collect all information.

Apart from replacing a patch for the former by two patches for latter,
this involved minimal adaptations of the lua scripts in the following
packages:

* gluon-announce
* gluon-announced
* gluon-mesh-batman-adv-core
* gluon-status-page

Always output empty objects or nothing at all where objects are expected, but
no elements exist.

Also remove a few unneeded "requires", a few basic modules are provided by
announce.lua by default.