Show warnings that non-static files are being used in static file directory

[ampersarnie]

When files that aren't static are being added to the static directory, we should think about throwing warnings with explainers of why they are not supported to make it explicitly clear at the time of parse/build. As we don't always know what a static file could be and the list is likely massive, we should probably work on a common exclusion list such as below and consider them non-static;

• .js
• .ts
• .php

[ampersarnie]

Implemented in release 1.2.0