- update target SDK to 31 and libraries to their latest version
- enable back PhotoViewDrawerLayout
- add PendingIntent flags and manifest entries required by target SDK 31
- update Travis config to API 31 build tools
- add missing experimental Kotlin API annotation.
- update compileSdkVersion, buildToolsVersion and targetSdkVersion to 30
- update Travis CI config file to use OpenJDK 11 on Ubuntu Focal and manual Android SDK components installation.