add 0 entries for agent types that don't exist at a time step

[gidden]

Currently, when agents have 0 entities in a time step, they don't get an entry in the time series of deployseries. This leads to figures like that attached. I think it would be better if they are given an entry for every time step.

[gidden]

note that this is a 10 time-step simulation, and that prey die off after timestep 2 and predators die off after time step 4.