Add changelog and bump version

Author: bbedward

android/fastlane/metadata/android/en-US/changelogs/81.txt

@@ -0,0 +1,4 @@
+- Add "Carbon" theme
+- Fix change representative not working sometimes
+- Auto-fill amount from deep-link/QR/NFC even if balance is insufficient
+- Misc. other fixes

ios/fastlane/metadata/en-US/release_notes.txt

@@ -1,5 +1,4 @@
-- Improve QR Scannability
-- Add Catalan, Norwegian, and Ukrainian translations
-- Add UAH currency conversion
-- Add nanocafe block explorer option
-- Misc bug fixes & improvements
+- Add "Carbon" theme
+- Fix change representative not working sometimes
+- Auto-fill amount from deep-link/QR/NFC even if balance is insufficient
+- Misc. other fixes

pubspec.yaml

@@ -6,7 +6,7 @@ description: Natrium - Fast, Robust & Secure NANO Wallet.
 # followed by an optional build number separated by a +.
 # Both the version and the builder number may be overridden in flutter
 # build by specifying --build-name and --build-number, respectively.
-version: 2.4.2+80
+version: 2.4.3+81
 
 environment:
     sdk: ">=2.11.99 <3.0.0"