Fix for "Blank map"

map.js
- The variable 'map' and object 'map' was in conflict.
- Changed the variable 'map' -> 'map_id'.
- 'data[i].id' doesn't exist, renamed it to 'data[i].uid'.
- Added the 'description' to function addMarkerToTrackline.

markers.php
- Added the variable $tmp["uid"] so map.js can use it.