Update README.md
Fixed a header image aspect ratio in landscape mode
Add hak as a contributor
Update contributors.png
Only shows a notification when the app is in background.
Merge pull request #25 from rejasupotaro/add_hak_as_a_contributor

Add hak as a contributor
Merge pull request #23 from hak/landscapeFixes

Fixed a header image aspect ratio in landscape mode
Removes a whitespace.
Extracts ActivityLifecycleObserver class, #26.
Removes unused imports.
Merge pull request #26 from mootoh/hide_notification_in_foreground

Only shows a notification when the app is in background.