purple: 3.0.x API removed chat_whisper
purple: update chat_send for 3.0.x API

Replaced message contents and flags with PurpleMessage.
purple: update send_im for 3.0.x API

Replaced message contents and flags with PurpleMessage.
srtp: parse encryption key from SDP
srtp: generate encryption key for each stream
srtp: offer encryption key when initiating a call
SRTP WIP