More intelligent caching in the app itself

[jbroadway]

The {# #} tags hard-code the compiled scripts/stylesheets into your templates, which is great for production. In development, using {! !} tags works, but will run the recompile step on each request, which can slow down development. The app should use caching based on file modification time internally as well, so it only recompiles when the scripts have changed (e.g., mtime of cached file < mtime of original).