Recovered Gradle build with latest release (ver. 4.10.2)

TravisCI
- Changed several apt configurations & build steps for Android

AndroidManifest:
- package name: fmt -> org.fmtlib

Gradle:
- Plugin version 3.1.3. Requires Gradle 4.4+
- Removed `x86` (duplicated with `x86_64`)
- `-std=c++17`. Latest NDK(clang7) should support this
- Missing `repositories` configuration

For some reason, the `repositories` config affects to the error:
"Could not find com.android.tools.lint:lint-gradle:26.1.3."