Add EF launchpad import (#1381)

## Issue Addressed

NA

## Proposed Changes

Adds an integration for keys generated via https://github.com/ethereum/eth2.0-deposit (In reality keys are *actually* generated here: https://github.com/ethereum/eth2.0-deposit-cli).

## Additional Info

NA

## TODO

- [x] Docs
- [x] Tests

Co-authored-by: Michael Sproul <michael@sigmaprime.io>

crypto/eth2_keystore/src/json_keystore/mod.rs

@@ -27,6 +27,7 @@ pub struct JsonKeystore {
     pub path: String,
     pub pubkey: String,
     pub version: Version,
+    pub description: Option<String>,
 }
 
 /// Version for `JsonKeystore`.