Display overlay screen for blocking operations (#186)

* Catch state error in homepage widget

* Add flutter_overlay_loader lib

- Displays an overlay screen to indicate blocking operation

* Wrap blocking widget transitions in a loading overlay

- Prevents user from doing other things while loading
- Shows the user that something is happening

* Linting fixes

* Show overlay when uploading attachment file

* Show overlay when downloading file also

* Show overlay when loading or submitting API forms

- Major improvements to usability "feel"

* UI improvements for stock item test results widget

* Fix API_FORM bug

- onSuccess function was not being called

pubspec.yaml

@@ -22,12 +22,13 @@ dependencies:
   flutter_localizations:
     sdk: flutter
   flutter_markdown: ^0.6.9                # Rendering markdown
+  flutter_overlay_loader: ^2.0.0          # Overlay screen support
   font_awesome_flutter: ^9.1.0            # FontAwesome icon set
   http: ^0.13.4
   image_picker: ^0.8.3                    # Select or take photos
   infinite_scroll_pagination: ^3.1.0      # Let the server do all the work!
   intl: ^0.17.0
-  one_context: ^1.1.0                     # Dialogs without requiring context
+  one_context: ^1.1.1                     # Dialogs without requiring context
   open_file: ^3.2.1                       # Open local files
   package_info_plus: ^1.0.4               # App information introspection
   path: ^1.8.0