* Router: Add a keyring for decrypting leases

...ole/java/src/net/i2p/router/web/ConfigKeyringHandler.java

...sole/java/src/net/i2p/router/web/ConfigKeyringHelper.java

apps/routerconsole/jsp/configkeyring.jsp

apps/routerconsole/jsp/confignav.jsp

core/java/src/net/i2p/I2PAppContext.java

core/java/src/net/i2p/util/KeyRing.java

router/java/src/net/i2p/router/PersistentKeyRing.java

router/java/src/net/i2p/router/RouterContext.java