Barcode scanner updates (#562)

* Add BUILDING.md

* Replace scaning library

- Out with qr_code_scanner
- In with flutter_zxing

* Update specs for jdk / kotlin / gradle

- NFI what this all means?

* Refactor barcode scanning widget

* Refactor barcode overlay

* Add handlers

* Update release notes

* Fix AppBar color

* Enhance attachment widget

* remove unused import

* Improved icon

* Select theme from main drawer

README.md

@@ -31,41 +31,4 @@ User documentation for the InvenTree mobile app can be found [within the InvenTr
 
 ## Developer Documentation
 
-For developers looking to contribute to the project, we use Flutter for app development. The project has been tested in Android Studio (on both Windows and Mac) and also VSCode.
-
-### Invoke Tasks
-
-We use the [invoke](https://www.pyinvoke.org) to run some core tasks - you will need python and invoke installed on your local system.
-
-### Getting Started
-
-Initial project setup (after you have installed all required dev tools) is as follows:
-
-Generate initial translation files:
-
-```
-invoke translate
-```
-
-Install required flutter packages:
-```
-flutter pub get
-```
-
-You should now be ready to debug on a connected or emulated device!
-
-### Building Release Versions
-
-Building release versions for target platforms (either android or iOS) is simplified using invoke:
-
-Build Android release:
-
-```
-invoke android
-```
-
-Build iOS release:
-
-```
-invoke ios
-```
+Refer to the [build instructions](BUILDING.md) for information on how to build the app from source.