Issue #457 - SeedPeers to use sipas DNS dumps

See issue #457 on Google Code.

* Changes to SeedPeers to read configured IPs of known peers from
  text files in JAR resource
* Fallback option for Android to specify an InputStream
* Unit test update for SeedPeers
* Gradle/Groovy script in contrib/seeds to download/build -seeds.txt for
  production network
* Hand-created -seeds.txt files for test net and unit test configs