Add knowledge commands to aios shell

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On aios shell, use /knowledge with subcommands to interactive with personal knowledge base:

• /knowledge add email Start a spider on email address, download all email and its archivements to ~/myai/email folder, and parse and embedding these emails into knowledge base;
• /knowledge add dir Scan a local folder, parse and embedding all files (sub folders not supported) in this folder into knowledge base. Also start watching this folder, if new file put into it, add to knowledge base automicly;
• /knowledge journal [topn] List latest top N journals of building knowledge base;
• /knowledge query $prompts Query input prompts from knowledge base, print prompt generated by knowledge;