Ethermint key generation (#78)

* WIP setting up Ethereum key CLI commands

* Functional key gen and showing Ethereum address

* Cleaned up changes

* WIP setting up Ethereum key CLI commands

* Functional key gen and showing Ethereum address

* Cleaned up changes

* Changed address to cosmos specific address

* Remove default bech32 prefixes and add basic add command test

* Changed Private key type to slice of bytes for compatibility and storability

* switch back to using cosmos crypto Keybase interfaces

* Changed key output to ethereum addressing instead of bitcoin and key generation to allow seeding from mnemonic and bip39 password

* Updated show command and added test

* Remove prefix requirement for showing keys and added existing keys commands to CLI temporarily

* Removed unnecessary duplicate code

* Readd prefixes for accounts temporarily

* Fix linting issue

* Remove TODO for setting PK to specific length of bytes (all functions use slice)

* Cleaned up descriptions to remove multi-sigs

cmd/emintd/main.go

@@ -28,6 +28,7 @@ func main() {
 	cdc := emintapp.MakeCodec()
 
 	config := sdk.GetConfig()
+	// TODO: Remove or change prefix if usable to generate Ethereum address
 	config.SetBech32PrefixForAccount(sdk.Bech32PrefixAccAddr, sdk.Bech32PrefixAccPub)
 	config.SetBech32PrefixForValidator(sdk.Bech32PrefixValAddr, sdk.Bech32PrefixValPub)
 	config.SetBech32PrefixForConsensusNode(sdk.Bech32PrefixConsAddr, sdk.Bech32PrefixConsPub)