A couple of fixes for demo_sph
Fix compatility with new API in demo_sph
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop

Conflicts:
	src/demos/irrlicht/demo_sph.cpp
A ChColorAsset can be created with a fast initialization in RGBA, ex
ChSharedPtr<ChColorAsset> myasset ( new ChColorAsset(0.5,0.3,0.4) );
Now a texture asset can be initialized to some filename right from the creation, so you do not need to call SetFilename later. Ex:
ChSharedPtr< ChTexture >  myasset ( new ChTexture ("C:\foo\bar.jpg" ));
Minor changes to these demos (comments, etc.)
The demo_collision.cpp contains an optional code for testing also the ChParticlesClones, updated to the new 'asset' system for visualization.
demo_convergence.cpp largely refactored:
- use the new 'asset' system approach to visualization,
- use the new ChBodyEasyXXX stuff that automatically computes masses and inertias.
The Irrlicht stuff is not intrusive anymore.
demo_conveyor.cpp largely refactored:
- use the new 'asset' system approach to visualization,
- use the new ChBodyEasyXXX stuff that automatically computes masses and inertias.
The Irrlicht stuff is not intrusive anymore.
demo_crank.cpp largely refactored:
- use the new 'asset' system approach to visualization,
- use the new ChBodyEasyXXX stuff that automatically computes masses and inertias.
The Irrlicht stuff is not intrusive anymore.
Larger 800x600 window for those two demos.
A few tweaks to the Chrono file utilities.

- change arguments to 'const char*' and 'char*', as appropriate
- change return type for ChFileutils::MakeDirectory():  return 0 if successful, +1 if directory exists, -1 otherwise
Add missing header.

The header file <cerrno> must be included for the declaration of errno.
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop

Conflicts:
	src/demos/irrlicht/demo_sph.cpp