Add a variable to toggle dev/production mode

[andrew-nguyen]

Right now, the only key difference is the call of setupCheckResponseTrigger(). If you're testing the add-on using the instructions in the readme, you'll run into an error unless you comment out the above call.

Adding a dev flag will cleanup the above problem and pave the way for other dev-only code we may add.

Requires changes to the readme also.

Current (suggested) differences between dev/prod code:

• Disable setupCheckResponseTrigger()
• Disable renaming of spreadsheet

[andrew-nguyen]

Instead of making this an explicit step, we should integrate this with #8 and make it part of a build spec.