Change MailsAdded/Removed into MailsChanged signal
Change MailsAdded/Removed into MailsChanged signal

The current signal method does not work very well since mail may be
added, changed and deleted at the same time. Using a MailsChanged signal
with a hash table of added/changed item and a list of removed mails IDs.
Also remove the useless structure for remove mails IDs.

Signed-off-by: Nicolas Dufresne <36c35e0aac84fcb59b447cc6415df42e7fda8df7@collabora.co.uk>

TelepathyIM/telepathy-spec,freedesktop-unofficial-mirror/telepathy__telepathy-spec