updated map related code to fix offline map bug

- in map.js : mapSetup function now takes an extra "mapServer" parameter
that allows to specify the mapServer to use
- in settings.js : settings.mapServers define online and offline 
map servers urls to use
- in map-online.html : mapSetup is now called with GM online server url
- in index.html : mapSetup is now called with GM online server url
- in map-offline : mapSetup is now called with local tiles directory
- in commons.js : map-offline has been added in the list of known pages