Support for theming in PHP templates has been dropped.
True theming should support theme inheritance, e.g. mytheme <- table <- default.
Currently, the Templating component does not support such inheritance. As the
only purpose of the themes so far was to style field groups with tables or
divs, and because automatic rendering of field groups/forms through the render()
method is discouraged and only recommended for rapid prototyping, themes are
dropped for now.
Because
* it's better for performance (no need to init form templates if there is no forms)
* right now, it crashes for all renderer except HTML (because the form templates obviously only exist for the HTML renderer)
The only other possible fix would be to force those resources to always use the HTML renderer
