Added option to save integrator stage data on a limited time interval

This is done to allow debugging of issues that occur only after a certain point
in the simulation without generating gigabytes of output files.
Saving intermediate integrator stage data no longer changes the solution
Added mathUtils::near function
Eliminated redundant implementation of Integrator::integrateToTime
Fixed Integrator::integrateToTime so it takes the right number of steps

Floating point rounding issues could previously cause the integrator to take one
more timestep than intended.
SCons 'mode' argument replaced with 'debug' and 'debug_symbols' options

This makes it possible to keep debug symbols even in an optimized version.
These settings are also stored in the ember.conf file, so they don't need
to be specified with every call to SCons.
Copy TBB.dll to the bin directory on Windows

This allows the GTest binary to run even when the TBB DLL is not installed
on a system path.
Fixed signed/unsigned warnings generated in assert statements