HD wallet: currentKey is now stable after serialization roundtrip

At the moment currentKeys map of KeyChainGroup is not restored after
deserialization and subsequent call to currentKey produces different
key then expected.
Proposed solution reconstructs currentKey map on deserialization using
stored numbers of issues keys. It is
not future-proof as it assumes only RECEIVE and CHANGE keys are being
used.
Add a method to deserialize a DeterministicKey from a byte-array rather than from the base-58 encoding thereof.
Update AUTHORS file with recent contributors
Add a missing lock on BasicKeyChain.getBloomFilter
Fix failing deserialization of wallet with an empty HD chain

Error occurred when deserializing wallet if either internal or external
zero account key chain of this wallet has no keys issued
Fix failing WalletProtobufSerializerTest
Make Transaction comparators compatible with equals
Add Alexykot's test net DNS seed. Tested using Bitcoin Wallet, works fine.
Merge branch 'master' of github.com:bitcoinj/bitcoinj