[FEAT]: More grid-like graph layout for the model diagram

[liunelson]

Is your feature request related to a problem? Please describe.
We've received some comments from users (particularly the UCSD team) about how the model diagrams are

• hard to read because of the swooping/looping edges
• emphasis on the transition nodes over the states
• hard to compare with diagrams in paper for validation since papers tend to use different layouts (grid-like)

In the case of the Zombie model:

• currently
  
• proposed
  

Describe the solution you'd like

• Do not use the transition nodes during the layout calculation
• Toggle the controller edges and rate law expressions (default = off, so users just want to quickly check if the Terarium model matches a paper's model)
• Pretty-print the SymPy rate law strings
• Larger arrow heads to make the state-to-state flow pattern more obvious
• Use hierarchical/Sugiyama layout algorithm to emphasize flow pattern?