Minor changes

[klappvisor]

• [x] Replac the field new_chat_member in Message with new_chat_members (the old field will still be available for a while for compatibility purposes).
• [x] Inline keyboards with switch_inline_query and switch_inline_query_current_chat can no longer be sent to channels because they are useless there.
• [x] New fields gif_duration in InlineQueryResultGif and mpeg4_duration in InlineQueryResultMpeg4Gif.