Changed XMLInput and Thermostat.
 - Small changes in Thermostat.
 - Added safety check in KineticEnergyHandler::compute().
 - Adjusted lennard-jones section of XMLInput.
 - Added thermostat to XMLInput.
 - Cleaned up example files.
Changed timing.
Added unit tests for Thermostat.
Implemented ResultOutput and ParticleFileReader.
 - Added classes ResultOutput and plotHandler_ResultOutput.
 - Replaced class ParticleInput_FileReader with ParticleFileReader.
 - Changed XMLInput, Particle, src/MolSim.cpp correspondingly.
 - Added a unit test for ResultOutput and ParticleFileReader.
 - Added and adjusted example XML files.