Avoid accidentally linking to telepathy-logger's private API

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=727162
empathy_tp_chat_new: take a GVariant for immutable properties
Adapt for group-members-changed giving details in a GVariant
EmpathyChat: rename handle_type to entity_type
Adapt for GVariant-based capabilities API
Modify McpAccountStorage implementations for GVariant-based dup_identifier
Remove tp_dbus_properties_mixin_iface_init which no longer exists

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77144
Update TPAW

+ TpawAvatarChooser: adapt for tp_account_dup_avatar_async