Upgrade Leaflet and fix issues with Location search and marker placement

* Upgrade Leaflet to 0.7.3
* Add a current location button using the leaflet-locatecontrol plugin to update the marker location
* Fix #42 - prevent enter from submitting CMS form and move marker when location is found
Merge pull request #47 from perfectsense/bugfix/location-marker

Upgrade Leaflet and fix issues with Location search and marker placement