Update Git submodules

* Update Boost and Urdl libraries.
* Remove broken submodule at '3rd.party/termbox'.
Insignificant modifications made in 'core' & 'python' libraries

* Auto-register aggregators (works only if building shared libraries).
* Tiny modifications to 'audiopia::resource' & 'audiopia::collection'.
* 2nd argument of the Python 'audiopia.collection' class's constructor is optional.