now the same names as in open source

The boundary conditions were in the wrong order. This caused effects at the edges of the fluid domain, which caused the the simulation to crash.

set defaults for gridPath and (out)Path
related #27 and #22

Moved Simulation::init() to Constructor, Simulation:free() to destructor and exchanged some members of Simulation with unique_ptr instances.

automatically set para->useStreams to false for single gpu