Merge pull request #1 from kakiang/dev

add feature for bookmarked articles

add features

rename some files

keep track of network calls by saving the time (in millisecons) requests are made to the database so that it's easy to decide whether we should make network calls or not based on the elapsed time between last network call and now

Add news category feature + clean up

Remove webfeed package; Simplify the article class by removing unnecessary proprieties; Use newsapi.org

abstract theme from codes into theme.dart

use Chrome Custom Tabs (flutter_custom_tabs plugin) to open web pages

fix issues related to the flow of execution. The initDB() function in database.dart had to be completely executed before any other operations. It wasn't the case, now it's fixed

code refactoring

change the bottomNavigationBar from BottomNavigationBar to BottomAppBar

refactor code

tweak theme (fonts)

Add NavigationControls to webview