Load signing configs from secret keystore file for gradle build.

signingconfigs.gradle

signingConfigs {
        debug {
            storeFile rootProject.file("signing/debug.keystore")
            storePassword "android"
            keyAlias "androiddebugkey"
            keyPassword "android"
        }

        release {
            def keystoreProperties = propertiesFrom("signing/keystore.properties")

            if (!keystoreProperties.isEmpty()) {
                storeFile file(keystoreProperties['storeFile'])
                storePassword keystoreProperties['storePassword']
                keyAlias keystoreProperties['keyAlias']
                keyPassword keystoreProperties['keyPassword']
            }
        }
    }