Large set of changes for v0.30

The examples weren't being properly tested in the last commit. When we fixed
that a lot of bugs in the new implementation of environment and agent were
found, which accounts for most of these changes.

The main difference is the mechanism to load simulations from a configuration
file. For that to work, we had to rework our module loading code in
`serialization` and add a `source_file` attribute to configurations (and
simulations, for that matter).

examples/mesa/mesa_sim.py

@@ -1,7 +1,7 @@
 from soil import Simulation
 from social_wealth import MoneyEnv, graph_generator
 
-sim = Simulation(name="mesa_sim", dry_run=True, max_steps=10, interval=2, model=MoneyEnv, model_params=dict(generator=graph_generator, N=10, width=50, height=50))
+sim = Simulation(name="mesa_sim", dump=False, max_steps=10, interval=2, model=MoneyEnv, model_params=dict(generator=graph_generator, N=10, width=50, height=50))
 
 if __name__ == "__main__":
     sim.run()

examples/mesa/social_wealth.py

@@ -53,7 +53,7 @@ class MoneyAgent(MesaAgent):
             self.give_money()
 
 
-class SocialMoneyAgent(NetworkAgent, MoneyAgent):
+class SocialMoneyAgent(MoneyAgent, NetworkAgent):
     wealth = 1
 
     def give_money(self):