Introduce experimental use of statically linked libRocket libs

This might be a short-term kludge; we are linking statically so that
we are able to start using both nomlib and libRocket in TTcards with a
minimum of packaging fuss for the project (statically linking here lets
us remove libRocket from the linking of TTcards, and just requires the
header files).

I'm not sure that it makes sense to abstract libRocket's higher-level
APIs...
Fix transparent spots in font rendering

* This affects rendered font text when taking screen dumps with
libRocketTest.
device_info: Add output of libRocket && OpenGL versions
Refactor libRocket initialization, Lua integration & more

* Introduce UIContext class interface for handling initialization
and removal of libRocket's context, debugger and SDL2 events
polling & translation.

* nom::init_librocket && nom::shutdown_librocket functions for
handling core initialization of libRocket (dep of UIContext init).

* Introduce unit test for basic Lua integration via libRocket
facilities.

* Introduce UIMessageBox class && unit test; this is an experimental
playground for the moment.

* Introduce RocketUtilities for providing smart ptr deleter functions
for automatic handling of libRocket's ElementDocument && Element
pointers, along with a namespace alias 'rocket' (Rocket::Core).

* types.hpp: Introduce Alignment::NONE type; this is for specialized
handling within UIMessageBox alignment methods (necessary for
translating between libRocket and nomlib).