Proposed changes to the senior / junior editing modes

[cschubiner]

•	Default to Fast Mode for Efficiency: For quick changes and straightforward coding, Aider would use the standard model.
•	Switch to Architect Mode When Needed: For more complex and deliberate coding tasks, Aider would activate the two-step Architect/Editor process.
•	Implementor Model for Fast Execution: The Implementor Model would handle direct application tasks efficiently, skipping the planning phase when unnecessary.