Clarify intent re code overrides in criteria for reviewing extensions.

Created by: universalhandle

Currently the criterion is:

The project does not override PHP, TPL, JS, or SQL from civicrm-core

It is clear to me how to override PHP or TPL code in an extension, but I am not aware of any way to replace core JS or SQL from an extension. So I guess the next questions are:

• Are there ways to do this, and if so what are they? Extension reviewers will need to know what to look for.
• If it's not currently possible, was the text was added because such capability is on the roadmap?
• If such capability is not on the roadmap, is there any reason not to delete JS and SQL from the sentence?