[feature/twig] Changing INCLUDEJS behavior

Was:
<!-- INCLUDEJS template/foo.js -->

Now:
<!-- INCLUDEJS T_TEMPLATE_PATH ~ '/foo.js' -->

Reasons for this:
1. INCLUDEJS is 3.1-dev only

2. INCLUDEJS has odd behavior to begin with (arbitrary setting root path
to styles/name/ directory)

3. INCLUDEJS could not include files from outside directories or anywhere
else

4. It was easier to change INCLUDEJS behavior to something more flexible
and useful than hack around it to make it work as it was with Twig.

PHPBB3-11598