便携设备GVG农情采样系统

Update the setting of the land cover classification system to allow use to switch different type of classification systems;
Update the map layers in the main page;
Fix the display order of historical data;
Fix the errors when selecting some land cover types;
Fix an issue of the abnormal refreshment of the location icon on the map;
Fix a bug that caused the program to exit abnormally due to network interruption;
Update the reminder for new version of the APP.