frontends (tools/webrtc): add a options to merge video for PiP and to specify size: - the `merge_pip` option is now used to indicate if local feedback and remote video streams must be merged with local feedback being a PiP of remote video. By default, it's done for `SINKS_AUTO`, but it can be manually specified to use it with `SINKS_APP` or to split ``SINKS_AUTO`` in 2 windows. - target size of the compositor used with `merge_pip` can be specified. By default, 720p is used. rel 428

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):
    ...