added seed command to get deterministic seed.

not yet password protected
remove help text about seed only displayed once
check its deterministic wallet before printing seed

when running the seed command
refactoring. get seed code in wallet2
query_key command in wallet rpc.

only support mnemonic as key_type currently
added viewkey command to CLI
added view_key to wallet RPC command query_key
Merge pull request #86 from jakoblind/seed

Query view key and seed