Jinja macro-centric refactor & organization

[dogversioning]

We've had several discussions about jinja macros for readability recently, and we're on board with more liberal use of them. This ticket is about trying to do this in a structured way - the google approach seems like a reasonable analog to what we should be thinking about.

While this does not need to be done in one go, generally we should follow these steps:

• When updating old templates, try to replace repeated/quirky control logic with macros
• If you're using the same macro more than one file, move that macro to someplace inside of ./cumulus_library/template_sql/macros, and import it from there
• if you're working on a downstream study, try to follow this same pattern, and merge shared, non-study specific macros back to the main library.

We'll close this issue by consensus when we feel like we've made enough progress on this that this pattern will be self-enforcing due to utility.

[dogversioning]

Not specifying the binning structure for macros just yet - @mikix , we should chat about this a bit more?

[dogversioning]

Addressed via #177