update progress handling in PgpDecryptVerifyOperation

- less progress messages overall
- report progress again based on input stream position, if filesize is known
- limit progress messages to one every 200ms while decrypting
- also fixed a bug in DecryptListFragment, the recycler view now reuses
  old views as intended instead of crossfading all the time.

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/InputData.java

@@ -23,6 +23,8 @@ import java.io.InputStream;
  * Wrapper to include size besides an InputStream
  */
 public class InputData {
+    public static final int UNKNOWN_FILESIZE = -1;
+
     private PositionAwareInputStream mInputStream;
     private long mSize;
     String mOriginalFilename;