Deprecate as, am, ac keywords for longer, more descriptive names

[Datseris]

I think we should deprecate the as, am, ac keywords of our main plotting function and call them instead agent_size, agent_color, agent_marker. Deprecation is easy for keyword arguments:

function f(; as = default, agent_size = as)
if as != default
@warn("as deprecated")
end
end

The rest of the keywords for the plotting function are not as cryptic.

[Datseris]

This should be done after #934 I pressume.