Support x86 and x86_64 devices

[pauledwardtang]

Currently, the abiFilters set in build.gradle prevent installation on emulators for testing and excludes devices like the Asus Zenphone 2 and Chromebooks (appropriate use case for a parent).

ndk {
    abiFilters 'armeabi-v7a', 'arm64-v8a'
}

From some prelim testing (in #392), I found that the APK size increases quite a bit (without splits configuration), about double the size, but no side effects other than that.

Is there a reason why these targets are excluded?