[commhistory-daemon] Replace notification context properties with a DBus interface

These properties are only ever used by the messaging and voicecall UIs
to indicate when inboxes/callhistory/conversations are observed, to
clear notifications. That doesn't require the use of contextkit or
statefs.

Instead, use the existing commhistory service and have clients call
methods on that directly.
[commhistory-daemon] Rename com.nokia.CommHistory dbus service to org.nemomobile.CommHistory
Parse dbus setObservedConversations arguments correctly
Merge pull request #14 from special/master

Replace notification context properties with a DBus service