add btFileUtils::toLower to convert a string (char*) to lower case
URDF import demo: add COLLADA .dae file support
add FiniteElementMethod demo, extracted from the OpenTissue library (under the zlib license)
don't crash if loading an invalid STL file
add comparison with Assimp for COLLADA file loading (disabled by default, to avoid library dependency)
Gwen: disable some flags that make the build incompatible
add btFileUtils::toLower to convert a string (char*) to lower case
URDF import demo: add COLLADA .dae file support
add FiniteElementMethod demo, extracted from the OpenTissue library (under the zlib license)
don't crash if loading an invalid STL file
add comparison with Assimp for COLLADA file loading (disabled by default, to avoid library dependency)
Gwen: disable some flags that make the build incompatible
fix Mac build
initialize variable to fix FEM nodes
add very basic multibody vehicle
tweak finite element experiment with parameter
render the tetrahedral mesh (no mesh normals)
placeholder for soft body
Refactored GJK, EPA and MPR as a template class, reducing/removing the dependencies
to the rest of the Bullet code base. This code will replace the original GJK/EPA
in a future commit.

Added btMprPenetration, an implementation of Minkowski Portal Refinement
by Daniel Fiser. Original MPR idea is by Gary Snethen, and the first
implementation is here: https://github.com/erwincoumans/xenocollide
It is an alternative to EPA, although computing the local penetration depth.
EPA computes the global penetration depth. In many cases, MPR is sufficient
and performs better than EPA.
Merge remote-tracking branch 'bp/master'

Conflicts:
	btgui/Bullet3AppSupport/CommonParameterInterface.h
disable work-in-progress softbody demo
Merge pull request #280 from erwincoumans/master

Minkowski Portal Refinement, Finite Element Method demo