big update

* Fixed it so that if you receive an invalid JSON message it won't kill
the connection to the broker.
* Moved some of the settings out to config.js file (need to work out how
to move google api key out to this file as well)
* added legend
* clicking on marker zooms in
* closing marker info zooms back out
* clicking on marker in legend zooms in on devices latest reported
update
* fixed some formatting
* updated some comments
* added new screenshot
Merge pull request #8 from matbor/master

big update