Add fast-forward feature to random number generator
Add Ecosystem#togglePause()

To freeze the ecosystem when I need another thread to read consistent
data (for example, during saving/loading of a petri dish, one of the
features I want to introduce next).
Pause the petri dish with P
Unpause petri dish when changing speed
Fix cycle in package dependencies
Fix problem with gradle install
More logical behavior of DelayNerve
Add Gson dependency to gradle build
Add serialization of nerves
Add serialization of food pieces
Add serialization of narjillos

This required a lot of changes to existing classes. Most of them (like
removing the stupid observer mechanism for narjillos movements and
deaths) are for the better.
Serialize entire DNA as a single string
Make Ecosystem abstract