v4.0.0

• Upgrade react-navigation to v5, use react-native-screens native stack for native stack navigator for performance gain
• Change navigation to bottom tab navigation
• Add Backup & restore settings and search history
• Add reading setting to view from right to left for image and novel viewer
• Add settings to hide image on trending search
• Fix novel reader missing text
• Switch crash reporting from fabric crashlytics to firebase crashlytics
• Save image as png
• Increase android minimum sdk version to 21 (Android 5)
• Rewrite some components with react hooks
• Write new components with react hooks
• Bug fix