:boom: [Fix] Revert chat templates with mannual version as nous-mixtral-8x7b behaves weirdly

:recycle: [Refactor] Use official chat_template to replace mannual parses for several models, and remove unused message split functions

:recycle: [Refactor] Move AVAILABLE_MODELS(_DICTS) to constants

:gem: [Feature] Support new model: openchat-3.5-0106

:gem: [Feature] New model enabled: gemma-7b

:boom: [Fix] Missing system message for original mistral models

:gem: [Feature] New model enabled: nous-mixtral-8-7b

:gem: [Feature] MessageComposer: Support openchat-3.5, and generalize preprocessing stages

:gem: [Feature] Support no-stream mode with dict response

:gem: [Feature] New MessageOutputer: Support Openai Stream format

:gem: [Feature] New MessageComposer: Merge and split messages in mixtral-instruct format