Added integrators (moved here from repex) and beginning of nose tests.
Added property retrieval for test systems temperature and pressure.
Removed unused _temperature and _pressure data.
Implemented automated test generation for integrators, testing a few steps with a harmonic oscillator.
Added stability test for a few steps of alanine dipeptide in implicit solvent.
Fixed incorrectly added doctest.
Corrected an error in periodicity and truncation in WCAFluid test.
Merge pull request #5 from jchodera/add-integrators

Added integrators (moved here from repex) and beginning of nose tests.