Part of namespac cleanup work.

Use TCP keepalive for detecting of connection goes offline in a more
reliable manner.

Keep track of known device and dump their info to cache. This should
speed up reconnect after restarting mconnect. The rationale is that the
devices are likely to be connected to to the local network and use
DHCP and as such will most probably get the same address the next time
they appear. Hence, it should be ok to attemp connection the last know
IP address. If that fails, the discovery process will still take place.

Currently notifications shown so far are not tracked, thus often it
happens that multiple notifications regarding the same topic appear,
where only one should be shown. The change adds tracking of
notifications being shown within the Notification class.

Notifications cleared by user will be re-shown if device pushes them
again.

If no time was provided in original message, use local time

Whenever a mobile device wakes up, it will send an identity packet from
the same IP, using different 'tcpPort' in the message. This should
prevent device from being closed and reconnected to too frequently.

Should display a shell notification. Skips notification from dialer,
these will likely be taken care of with telephony plugin.