Update: Add support for su3-signed development builds (ticket #1381)

Full version is used as the su3 version.
Uses same su3 certs as release updates. Users may add additional certs
to ~/.i2p/certificates/router/ as necessary.
Copy echelon's reseed key for use as a router signer.
Unsigned update remains a separate option for now.
Various update subsystem cleanups.

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 16;
+    public final static long BUILD = 17;
 
     /** for example "-test" */
     public final static String EXTRA = "";