BUG: turned off gravity when creating internal force model to avoid doubling gravity; changed indices of fixed nodes to 0-based; changed default material property

Clean up inter-library dependencies (some are already propogated through immediate dependencies)

BUG: fixed a bug in NewtonSolver that limits num of iterations to 1; added test case for NewtonSolver; renamed file imstkNonlinearSystem to be consistent;

Move the impl to avoid compilation errors
occuring due to recent use of forward declerations

Move make_unique definition to the common library

Add options to disable sinks in simulation manager
Make logger singleton