Places from location are dynamically loaded

When a location (defined by its lat lon) became visible on the map, its places are retrieve (via .json file) and displayed.

In order to do that, all location are defined on a dedicated json file (locations.json) that is loaded when you access the map..
Remove location info from specific location files

those information are already defined in the locations.json file and retreived from it.
Check if location is already displayed when displaying

the check is now done when asked for display info about a location and no more when trying to figure if location is on the map or not.
So that, when you ask for displaying places from a location, you don't have to thing about it, it is the responsabilité of the display to do that.
added a sample of location, with complete "place" JSON object. (allegedly, to be completed)
mandatory fields (am I right?)
Update readme with new locations.json file
Improve readme.

Thanks @brunobord for your usefull advices.
Merge pull request #62 from avernois/dynamic_loading

Dynamic loading