Centralized jinja template entrypoint

[dogversioning]

This PR makes the following changes:

• template_sql/base_templates now has a single entrypoint for rendering templates
  • This also supports loading templates from designated folders
  • As a result, everything going through this now gets access to macros
• reorged all template renderers to go through this entrypoint
• moved statistics templates to be a subfolder of statistics for pattern standardization

Checklist

• Consider if documentation (like in docs/) needs to be updated - They do, I'm going to do that in one go.
• Consider if tests should be added
• Update template repo if there are changes to study configuration

[dogversioning]

I decided to not go crazy on moving additional macro snippets into shared locations, but it should be simple to do that going forward now.