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)

src/controller/image/generation.rs

@@ -6,7 +6,7 @@ use crate::agent::AgentPurpose;
 use crate::agent::ControllerTrait;
 use crate::agent::provider::ImageGenerationParams;
 use crate::controller::utils::agent::get_effective_agent_for_purpose_or_complain;
-use crate::controller::utils::mime::get_file_extension;
+use crate::utils::mime::get_file_extension;
 use crate::conversation::create_llm_conversation_for_matrix_thread;
 use crate::conversation::matrix::MatrixMessageProcessingParams;
 use crate::strings;
@@ -43,7 +43,7 @@ pub async fn handle_image(
     );
 
     let conversation = create_llm_conversation_for_matrix_thread(
-        matrix_link.clone(),
+        &matrix_link,
         message_context.room(),
         message_context.thread_info().root_event_id.clone(),
         &params,