Dynamic variable fields

Support dynamic fields such as {first_name}, etc around Featurebase:

• Workflows - can create personalized workflows

• Macros - would be super powerful to have dynamic macros

• Changelog - can create a personalized intro

• Surveys - can create a personalized survey

• Links - always show the right link based on attribtues

• etc,

This would allow for much more advanced and personalized communication.