update: refactor and add loading page class

app/lib/pages/default_page.dart

app/lib/pages/loading_page.dart

app/lib/widgets/choropleth_map.dart

app/lib/widgets/main_layout.dart

app/pubspec.yaml

server/APIs/__pycache__/get_weather.cpython-311.pyc

server/APIs/__pycache__/get_weather.cpython-39.pyc

server/APIs/get_weather.py

server/database/icedb

server/database/schema.sql

server/main.py

server/map_handler/__pycache__/add_lake.cpython-311.pyc

.../map_handler/__pycache__/get_measurements.cpython-311.pyc

server/map_handler/__pycache__/get_sat_query.cpython-311.pyc

...er/map_handler/__pycache__/input_new_data.cpython-311.pyc

server/map_handler/__pycache__/input_new_data.cpython-39.pyc

server/map_handler/__pycache__/process_lake.cpython-311.pyc

server/map_handler/add_lake.py

server/map_handler/get_measurements.py

server/map_handler/input_new_data.py