Add "scaffold" option for generated files

[pkedy]

This PR adds the --scaffold option to apex generate. This option allows an Apex configuration (and plugins) to defer generation of "scaffolded" files until the Apex spec is ready. This is important because once scaffolded files are generated, they cannot be regenerated because the developer would lose their changes.

Config example

generates:
  my_service.go:
    ifNotExists: true
    scaffold: true
    module: 'https://deno.land/x/apex_codegen@v0.1.9/go/mod.ts'
    visitorClass: ScaffoldVisitor

The developer runs apex generate --scaffold to include the generation of these files.

Other miscellaneous improvements:

• Version bumps for std and dax
• Removed dead code and fixed tests with remnants of shorthand tasks
• Fixed bug where tables were being rendered twice