Rethinking thermostats

[J-Hizzle]

Solves #62.

I

1. deleted the former BBK-like implementation in LangevinThermostat.cpp;
2. implemented a local thermostatting scheme in the BAOAB VelocityVerletLangevinThermostat.cpp;
3. Generalized the VelocityVerlet and VelocityVerletLangevinThermostat schemes in the newly implemented UpdateSteps.hpp module.

A user may now built their own integrator by combining the drift, kick and Ornstein Uhlenbeck update steps or even add new update steps if necessary.