Fixes small typo in a comment explaining an equation
Provided names to elements, provided nondefault values for masses

Helped me with the debugging, to see who's worked on, how values are computed and populating terms in the EOMs, etc.
Avoids inquiring about the size of two vectors (constraints and variables) at each iteration of several loops.
small typo in comment fixed
The fonts for Irrlicht are load from sudirectory fonts/ in directory specified with the global "irrlicht_default_obj_dir" (that the user can change from default "../data/").
Previously it was hardcoded into "../data/fonts/" and could not be changed, that was potentially a problem if one needed to have a data directory with a path different than ..data/
Improvement to readability and avoids gnu gcc warnings.
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop
New system for processing particles (moving flows of bodies).
It is based on ChParticleProcessor. One can plug into this processor object two components:
- a ChParticleEventTrigger (there are a few children classes, ready to use; ex. trigger when entering a box)
- a ChParticleProcessEvent  (there are a few children classes, ready to use; ex. remove from simulation, count, etc.)
More will be added in future.
Change arguments of various functions for setting inertia matrices to const refs.
Cleanup related to ChBody::GetFrame_COG_to_abs() and ChBody::GetFrame_REF_to_abs().
Return the body lists of markers and forces as const references.

This actually prohibits changing the lists through these functions (which was previously "enforced" through a comment in the header file).
Remove old unused code.
Return const references to the lists of bodies and links of a ChAssembly.
More cleanup in ChBody (mostly const-related)
Cleanup of ChBodyDEM and ChBodyAuxRef.
Remove `using namespace collision` from ChBody.h
Fix irrlicht demos (now that chrono::collision is not available through ChBody.h)
Cleanup `ChMaterial.h` and `ChVsualization.h`

- remove using directives
- use cont references where appropriate
- reformatting (untabify)
Place all classes in `particlefactory` in the namespace `chrono::particlefactory`

Without this, the implementation depended implicitly on the `chrono` namespace being available through a using declaration in one of the included headers.
Moreover, it is appropriate for all Chrono classes to be defined within the main `chrono` namespace.
Fix issues related to the `chrono` namespace not available anymore through some included header.

NOTE: this is a fix consistent with current implementation of the rest of the irrlicht_interface. A better fix is to define all classes in this module within the main `chrono` namespace.