clean up messagehandler a bit

remove unused cruft. rename registerSender function to
createRegisterMessage to reflect that it really only creates that message.

Jira-issue: WP-850
more messagehandler cleanup

use strings for setting routes by fixing how Array.join is used. rename ownId
to ownSessionId, including the setter and getter.

Jira-issue: WP-850
remove duplicated code in messagehandler

use function for getting the PZH sesssion id

Jira-issue: WP-850
drop msgs if local wrt disconnected

if received msg is intended for wrt connected to this pzp, do not forward msg
back to pzh. fixes infinite msg loop.

Jira-issue: WP-851
signal pz sender than receiver disconnected

send a message to the original sender in case the original receiver disappeared.
upon receiving such a message all registered RPC services are notified of the
sessionId that disconnected. this allows the services to stop trying to send
messages to this sessionId.

Jira-issue: WP-851
implement disconnect event for geolocation api

for geoip module, clear timer for sending position updates to a disconnected
session id.

Jira-issue: WP-851