MDL-69087 core_h5p: add renderer to let personalize styles

MDL-69087 core_h5p: add renderer to let personalize styles

Existing mod_hvp pluging has a renderer to let Moodle instances
alter styles, Javascript, semantics (fields in the editor) and
content: https://github.com/h5p/moodle-mod_hvp/blob/stable/renderer.php

The approach for core_h5p is exactly the same, to let people
to reuse their existing code.