Build update (#495)

* package and build updates
* add sdk preview license to build
* use build tools 26.0.2
* use different libgmp mirror

src/main/java/io/lbry/browser/LocalFileProvider.java

@@ -0,0 +1,7 @@
+package io.lbry.browser;
+
+import android.support.v4.content.FileProvider;
+
+public class LocalFileProvider extends FileProvider {
+
+}