Fetch stories from U-Report's public API

[nathanbaleeta]

Considering the documentation on U-Report's public API that features stories, assets, etc from the website:

Using the http package, for this type of work, carry out the following steps:

• [x] Create a new branch from develop called fetch-stories. Hint: git checkout -b <new-branch> <existing-branch>
• [x] Add the http package.
• [x] Make a network request using the http package to the stories endpoint.
• [x] Convert the response into a custom Dart object called Story.
• [x] Fetch the data, ensure fetchStory() is called inside initState().
• [x] Display the data with Flutter.
• [x] Commit the changes (as a single commit).
• [x] Push changes to github. Hint: git push --set-upstream origin fetch-stories
• [x] Open a pull-request.

PS: This link offers a handy tutorial on the same.