Cleanup and bug fixes

[dougollerenshaw]

Changes to clean up code and fix some bugs:

• Changed exponential plot example text
• Moved system prompt to constants
• Removed unused logic for detecting truncated responses
• Avoided calls to on_version_change method while rebuilding version dropdown contents
• Improved parsing logic for json responses to limit the need for retries
• Removed some unnecessary constants and comments from constants.py