Displays time realtime, ability to jump around in time

Time is now displayed in top left corner of the window. It changes to accommodate for fast forwarding and for jumping in time.
Note that currently, time is an arbitrary number that starts at 0 when the simulation starts

The user is now able to jump to a certain point in time using the text input box and the "jump!" button underneath it. The user needs to enter the time they want to go to in the input box and press jump.
Note that this feature only works with positive values of time.

If the objects don't seem like they are moving it might be because they are moving too slowly to see, try fast forwarding to see motion.

Thanks!

added a null check for both currentTime and systemTime