* core/types: make Signer derive address instead of public key
There are two reasons to do this now: The upcoming ethclient signer
doesn't know the public key, just the address. EIP 208 will introduce a
new signer which derives the 'entry point' address for transactions with
zero signature. The entry point has no public key.
Other changes to the interface ease the path make to moving signature
crypto out of core/types later.
* ethclient, mobile: add TransactionSender
The new method can get the right signer without any crypto, and without
knowledge of the signature scheme that was used when the transaction was
included.
This significantly reduces the dependency closure of ethclient, which no
longer depends on core/vm as of this change.
All uses of vm.Logs are replaced by []*types.Log. NewLog is gone too,
the constructor simply returned a literal.
* build: modify the iOS namespace to iGeth (gomobile limitation)
* mobile: assign names to return types for ObjC wrapper
* mobile: use more expanded names for iOS/Swift API
ethclient now returns ethereum.NotFound if the server returns null and
no error while accessing blockchain data.
The light client cannot provide arbitrary transactions. The change to
split transaction access into its own interface emphasizes that
transactions should not be relied on and recommends use of logs.
