tools (common/template): add filter to get media types: Add 2 filters to get main type and subtype of media type. Jinja2 and Nunjucks don't handle slices in the same way (Python way for Jinja2, JS way for Nunjucks), making it difficult to retrieve main type of a media from media type. Thoses filters work in both cases.

from typing import Optional

from twisted.words.xish import domish


class BaseError(Exception):
    namespace: str
    condition: str
    text: Optional[str]
    textLang: Optional[str]
    appCondition: Optional[domish.Element]

class StanzaError(BaseError):
    ...