Add WebBluetoothGloballyDisabled exception and fix availability state (#165)

* Add WebBluetoothGloballyDisabled exception and fix availability state

* Update changelog and version

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Co-authored-by: Foti Dim <foti@navideck.com>

pubspec.yaml

@@ -1,6 +1,6 @@
 name: universal_ble
 description: A cross-platform (Android/iOS/macOS/Windows/Linux/Web) Bluetooth Low Energy (BLE) plugin for Flutter
-version: 0.19.0
+version: 0.20.0
 homepage: https://navideck.com
 repository: https://github.com/Navideck/universal_ble
 issue_tracker: https://github.com/Navideck/universal_ble/issues
@@ -31,7 +31,7 @@ dependencies:
   flutter:
     sdk: flutter
   plugin_platform_interface: ^2.1.6
-  flutter_web_bluetooth: ^1.0.0
+  flutter_web_bluetooth: ^1.1.0
   bluez: ^0.8.3
 
 dev_dependencies: