[FEATURE] please consider allowing configuration and/or mailto: for share

[neiljaywarner]

Please consider configuration for share. e.g.

1. using share mailto should allow mac to work according to shareplus pub.dev site
2. allowing a default share app would be nice, and/or even a default mailto address

eg use case

1. Mac support for no worry about pipeline for preprod work
2. more easily allow for quick share to jira, share to dev email etc

Important note: alice does work on mac as is out of the box just not for share or save share gives MissingPluginException(No implementation found for method share on channel plugins.flutter.io/share) #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7)

save gives [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: MissingPluginException(No implementation found for method checkPermissionStatus on channel flutter.baseflow.com/permissions/methods) #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7) #1 MethodChannelPermissionHandler.checkPermissionStatus (package:permission_handler_platform_interface/src/method_channel/method_channel_permission_handler.dart:16:20) #2 AliceSaveHelper._checkPermissions (package:alice/helper/alice_save_helper.dart:32:20)