Provide a Tor/obfsproxy arm64 binary
Starting August 1, 2019, all new apps and app updates that include native code are required to provide 64-bit versions in addition to 32-bit versions when publishing to Google Play.
We currently do not provide 64-bit binaries of Tor and obfsproxy for arm and x86, but should do so.
As the APK size will get quite big with the additional binaries, we should consider split APKs (#1278).