Initial work on Vision support in text conversations and Image Editing

This is a huge patch which does some major refactoring like:

- renaming "Image Generation" to "Image Creation" in most places,
  to better match its new command (`!bai image create`)

- relocating image creation command (`!bai image` -> `!bai image create`),
  so it wouldn't conflict with the new image editing command (`!bai image edit`)

- introducing a new image editing command (`!bai image edit`), which
  is meant to work only with the OpenAI provider, but doesn't fully work yet
  due to https://github.com/64bit/async-openai/issues/364, though a next patch will fix it

- adding support for reading images off of Matrix conversations and forwarding them to
  text conversations. Works for OpenAI, but not for Anthropic yet
  (requires custom patches) and not for OpenAI-Compat (no support for
  images there)

- relocating some utils around (base64, mime)

docs/configuration/README.md

@@ -40,7 +40,7 @@ You can adjust the following settings per room and/or globally:
 - [💬 Text Generation](text-generation.md)
 - [🦻 Speech-to-Text](speech-to-text.md)
 - [🗣️ Text-to-Speech](text-to-speech.md)
-- [🖌️ Image Generation](image-generation.md)
+- [🖌️ Image Creation](image-generation.md)
 - [🤝 Handlers](handlers.md)
 
 Refer to the bot's help messages (as a response to a `!bai config` help command) for the most up-to-date information on what Room Settings can be configured.