Merge branch 'feature/keys' of https://github.com/ethersphere/go-ethereum into ethersphere-feature/keys

Conflicts:
	.gitignore
	README.md

- remove lib   *EthLib, expose gui itself to initial import window
- remove addr []byte instead use dynamic adress()
- use ethereum.KeyManager to retrieve address and privateKey
- add Session string (keyRing identifier)
- add and reimplement ImportAndSetPrivKey and CreateAndSetPrivKey

main loop uses new flags and common methods in util: db, keymanager set up; passes KeyRing/Session string to gui

- keyring: keyring/session identifier used by key manager
- keystore: choice of db/file key storage
- import message updated
- export: name of directory to export keys to (was bool)

- keyring: keyring/session identifier used by key manager
- keystore: choice of db/file key storage
- import message updated
- export: name of directory to export keys to (was bool)

- keypair, keyring:
-- consistent naming of methods
-- error propagation
-- no panic
- keyManager: persist, import, export, initialize and (re)set keyring
- no global public "singleton" keyring, instead interface via keyManager
- keys test
- KeyStore interface, DB and File store implementations