Centralize time zone code in DataHelper

...2psnark/java/src/org/klomp/snark/web/I2PSnarkServlet.java

apps/i2ptunnel/java/src/net/i2p/i2ptunnel/ConnThrottler.java

...uterconsole/java/src/net/i2p/router/news/NewsManager.java

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

...erconsole/java/src/net/i2p/router/web/EventLogHelper.java

...erconsole/java/src/net/i2p/router/web/NewsFeedHelper.java

...nsole/java/src/net/i2p/router/web/SummaryBarRenderer.java

apps/susidns/src/java/src/i2p/susi/dns/FormatDate.java

apps/susimail/src/src/i2p/susi/webmail/Mail.java

core/java/src/net/i2p/data/DataHelper.java

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