Support custom CRS

[maRci002]

Hello guys, me and @fegyi001 made avaible to use custom CRS in this project with help of proj4dart project (we are the authors of it).

Proj4Crs and Proj4Projection classes based on Proj4Leaflet project and it has BSD 2-Clause "Simplified" License so we need to make sure we can use their codebase.

We also added some support for multiple origins based on this commit (which is still not reviewed but I tested this feature on this map and the map isn't bouncing unlike in Leaflet's map 👌).

We made an example page which uses EPSG:3413 crs.

Closes #514

[maRci002]

The only problem occurs if you try to over zoom / over unzoom, but the app doesn't crash or there isn't any flutter red error screen, just your console is being flooded 😄

You cannot over zoom via double taps only with double finger scale. I think this problem shouldn't be fixed on this level because I assume num scale(double zoom) { will have max value based on maxZoom and at least 0 value.

Over unzoom:

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following RangeError was thrown while handling a gesture:
RangeError (index): Invalid value: Not in range 0..8, inclusive: -1

When the exception was thrown, this was the stack: 
#0      List.[] (dart:core-patch/array.dart:15:52)
#1      Proj4Crs.scale (package:flutter_map/src/geo/crs/crs.dart:293:30)
#2      Proj4Crs.pointToLatLng (package:flutter_map/src/geo/crs/crs.dart:258:22)
#3      MapState.unproject (package:flutter_map/src/map/map.dart:238:24)
#4      MapGestureMixin.handleScaleUpdate.<anonymous closure> (package:flutter_map/src/gestures/gestures.dart:73:29)
...
Handler: "onUpdate"
Recognizer: ScaleGestureRecognizer#3b3f6
  debugOwner: GestureDetector
════════════════════════════════════════════════════════════════════════════════════════════════════

Over zoom:

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following RangeError was thrown while handling a gesture:
RangeError (index): Invalid value: Not in range 0..8, inclusive: 9

When the exception was thrown, this was the stack: 
#0      List.[] (dart:core-patch/array.dart:15:52)
#1      Proj4Crs.scale (package:flutter_map/src/geo/crs/crs.dart:294:30)
#2      Proj4Crs.pointToLatLng (package:flutter_map/src/geo/crs/crs.dart:258:22)
#3      MapState.unproject (package:flutter_map/src/map/map.dart:238:24)
#4      MapGestureMixin.handleScaleUpdate.<anonymous closure> (package:flutter_map/src/gestures/gestures.dart:73:29)
...
Handler: "onUpdate"
Recognizer: ScaleGestureRecognizer#40141
  debugOwner: GestureDetector
════════════════════════════════════════════════════════════════════════════════════════════════════

[johnpryan]

This looks good to me, ready to merge?

[maRci002]

Yes 😃

Just take a test ride with mentioned review and use zoom / scalelayer plugins.

Edit:

  ScaleLayerPluginOption(
	lineColor: Colors.blue,
	lineWidth: 2,
	textStyle: TextStyle(color: Colors.blue, fontSize: 12),
	padding: EdgeInsets.all(10),
  ),
  ZoomButtonsPluginOption(
	minZoom: 1,
	maxZoom: maxZoom.toInt(), // Don't forget to adjust maxZoom
	mini: true,
	padding: 10,
	alignment: Alignment.bottomRight,
  ),

And go to zoombuttons_plugin_option.dart
And change line 65:
From:
zoom = zoomButtonsOpts.minZoom as double;
To:
zoom = zoomButtonsOpts.minZoom.toDouble();

Sometimes as double throws exception even at ZoomButtonsPlugins page:
type 'int' is not a subtype of type 'double' in type cast

[maRci002]

Forget about zoom problems this PR resolves another problem. So yes I am ready to merge.

[savasadar]

Hello @maRci002, I am living a problem about the create a new projection with yandex map tiles.
Could you help?
#642