Template System

[avdi]

For this to be a reusable app, it must be possible for the user to make customizations to e.g. the standard *.scss files. Right now that's not possible.

Quarto needs a template subsystem whereby a template for a given build file can be found either a) within the gem; or b) within the user's project directory, probably in .quarto/templates. With preference given to the project directory, if the template exists there. Further, it should be possible to easily ask Quarto to make an initial copy of its templates into the .quarto/templates directory, either all at once or pieacmeal, for user customization.