[RCD] Roundcube Framework and BC breaks list

I've started working on the framework. The list of backward compatibity breaks will be long. Here's the first part.

Renamed functions:

rcube_imap::decode_address_list() > rcube_mime::decode_address_list() rcube_imap::decode_mime_string() > rcube_mime::decode_mime_string() rcube_imap::decode_header() > rcube_mime::decode_header() rcube_imap::mime_decode() > rcube_mime::decode() rcube_imap::explode_header_string() > rcube_mime::explode_header_string() rcube_imap::unfold_flowed() > rcube_mime::unfold_flowed() rcube_imap::format_flowed() > rcube_mime::format_flowed()

Removed functions:

rcube_imap::select_mailbox() rcube_imap::in_searchset() rcube_imap::id2uid()