Run simulations in soft real time

[kyllingstad]

For hardware-in-the-loop and human-in-the-loop simulations, Coral must be able to synchronise logical time with wall clock time. It should be possible to specify a constant ratio between these, where 1 would mean that the simulation runs in real time, while 2 means it runs twice as fast.

By "soft real time" I mean that Coral only sets an upper bound for the speed. Any slave which is not able to perform its calculations fast enough will still slow the entire simulation down.

Some hardware-in-the-loop applications may require hard real time synchronisation. FMI does not currently support this (i.e., there is no way to tell a slave how much real time it gets to perform a time step), but there may be ways to work around it; see issue #2.