generate app should not populate wp-content/themes

[leedxw]

whippet generate app currently populates /wp-content/themes/theme with a theme that depends on access to a premium plugin. It would be better if there was a command the just generated a bare-bones framework, given whippet generate theme exists.

[snim2]

• By default generate empty theme with an index.php file
• Add CLI option to generate app with template theme