fix(example): replaced EPSG:3413 with EPSG:3996 (fixed imagery source) & removed Custom CRS page (#1992)

* Replaced EPSG:3413 example with EPSG:3996 with fixed imagery source

* Remove removed asset from pubspec

* Removed defunct Custom CRS page from example
Transferred documentation readme to website

---------

Co-authored-by: mootw <[email protected]>

Author: JaffaKetchup

example/assets/map/epsg3413/amsr2.png

@@ -3,9 +3,8 @@ import 'package:flutter_map_example/pages/animated_map_controller.dart';
 import 'package:flutter_map_example/pages/bundled_offline_map.dart';
 import 'package:flutter_map_example/pages/cancellable_tile_provider.dart';
 import 'package:flutter_map_example/pages/circle.dart';
-import 'package:flutter_map_example/pages/custom_crs/custom_crs.dart';
 import 'package:flutter_map_example/pages/debouncing_tile_update_transformer.dart';
-import 'package:flutter_map_example/pages/epsg3413_crs.dart';
+import 'package:flutter_map_example/pages/epsg3996_crs.dart';
 import 'package:flutter_map_example/pages/epsg4326_crs.dart';
 import 'package:flutter_map_example/pages/fallback_url_page.dart';
 import 'package:flutter_map_example/pages/home.dart';
@@ -70,7 +69,6 @@ class MyApp extends StatelessWidget {
         PolygonPerfStressPage.route: (context) => const PolygonPerfStressPage(),
         SlidingMapPage.route: (_) => const SlidingMapPage(),
         WMSLayerPage.route: (context) => const WMSLayerPage(),
-        CustomCrsPage.route: (context) => const CustomCrsPage(),
         TileLoadingErrorHandle.route: (context) =>
             const TileLoadingErrorHandle(),
         TileBuilderPage.route: (context) => const TileBuilderPage(),
@@ -79,7 +77,7 @@ class MyApp extends StatelessWidget {
         MapInsideListViewPage.route: (context) => const MapInsideListViewPage(),
         ResetTileLayerPage.route: (context) => const ResetTileLayerPage(),
         EPSG4326Page.route: (context) => const EPSG4326Page(),
-        EPSG3413Page.route: (context) => const EPSG3413Page(),
+        EPSG3996Page.route: (context) => const EPSG3996Page(),
         ScreenPointToLatLngPage.route: (context) =>
             const ScreenPointToLatLngPage(),
         LatLngToScreenPointPage.route: (context) =>