Util: Move RFC822Date from router to core for SusiMail

...erconsole/java/src/net/i2p/router/update/NewsFetcher.java

...java/src/net/i2p/router/update/UnsignedUpdateChecker.java

.../java/src/net/i2p/router/update/UnsignedUpdateRunner.java

core/java/src/net/i2p/util/RFC822Date.java

...er/java/src/net/i2p/router/networkdb/reseed/Reseeder.java