add misc functionalities for supporting gazebo
add some functions for gazebo support
Adapt the CI script for the move of the repo.
The new constraintDynamics handles contact and constraint forces simultaneously. The contactDynamics is still functional (and many apps still depend on it) but I plan to phase it out once I integrate constraintDynamics with jointLimitDynamics
support gazebo
Merge pull request #53 from dartsim/gazebo_support

Gazebo support
modified simulation::World; added simulation::SimWindow; rewrote forwardSim app such that it uses simulation::World data structures
added simulation::SimWindow
fix bug: SkeletonDynamics::setInternalForces(...) set the internal forces as zero always because the default values of internal forces's min/max allowance was zero. Now the default values are -1e9 and 1e9.
fix bug: SkeletonDynamics::setInternalForces(...) set the internal forces as zero always because the default values of internal forces's min/max allowance was zero. Now the default values are -1e9 and 1e9.
Changing World class interface.
replace 1e9 to std::numeric_limit<double>::infinity()
Merge remote-tracking branch 'refs/remotes/origin/master' into gazebo_support

Conflicts:
	src/simulation/World.cpp
merge from master branch
Merge pull request #55 from dartsim/gazebo_support

Gazebo support
change the interface of World class.
Skeleton has mInitPose and SkeletonDynamics has mInitQDotVector. SkeletonDynamics is able to backup its state with backupInitState() and restore with restoreInitState().

World is able to reset the states of all skeletons with reset(().

TODO: We can consider better ways for this functionalities.
Merge pull request #56 from dartsim/gazebo_support

change the interface of World class.
fixed a bug in World::setState; modified cube to use world class
rewrote balance app