Add Java package name to nanopb.proto.

This fixes problems when interoperating with Java.

Fix suggested by trepidacious:
https://groups.google.com/forum/#!topic/nanopb/hZgrj6h9OnY

generator/nanopb.proto

@@ -7,6 +7,8 @@
 
 import "google/protobuf/descriptor.proto";
 
+option java_package = "fi.kapsi.koti.jpa.nanopb";
+
 enum FieldType {
     FT_DEFAULT = 0; // Automatically decide field type, generate static field if possible.
     FT_CALLBACK = 1; // Always generate a callback field.