Automatic swap refund bot

[denalimarsh]

Introduces RefundBot, a swap refund process that scans Kava and Binance Chain for refundable swaps and automatically processes them. Works on testnet. Once approved, I'll launch a server for RefundBot and put it live on mainnet. Edit: RefundBot is live on mainnet.

Example testnet refund cron routine output:

[2020-06-15T08:51:32.754Z] Kava refundable swap count: 1
[2020-06-15T08:51:32.757Z]      Refunding swap 251165847a4f65efe47174339b76cf65f817e5fd700018d51a8dad89e4b2ec1f
[2020-06-15T08:51:32.790Z]      Tx hash: D3F38B67C2E0BF073E1BC1111CAEF09F81141B1DA568C2C462AE3E909B4F2D6E
[2020-06-15T08:51:39.458Z] Binance Chain refundable swap count: 8
[2020-06-15T08:51:39.458Z]      Refunding swap 5a044d1e9fe39f1065a61bfa2dc66b3ead80ddf84b960f8fbbfc7d39609bad10
[2020-06-15T08:51:40.789Z]      Tx hash: 541F78A34A4BDCE69F8ECE61E362681C47D17746AC43C2F5D3ED7F6602615FBA
[2020-06-15T08:51:43.793Z]      Refunding swap 130cd8ec49960989343f7988c7d728959ad8e8fbca363350d32bb7ff418d1252
[2020-06-15T08:51:45.239Z]      Tx hash: 4EB31E241535EEAA3095CB96EEC7446CB0E28441A570856078ADB071F015FCEC
[2020-06-15T08:51:48.243Z]      Refunding swap eb69463cc2063d230ec9079b91495c309c68ccdf7d8811db1aa488ee72a64dbd
[2020-06-15T08:51:48.879Z]      Tx hash: 68982CEC5F3EC870CC9018CA99C89E289E6854C135573850082C70474128361D
...

The RefundBot waits 3 seconds between posting refund txs to Binance Chain, otherwise, an account sequence error is thrown. I've created #14 for upstreaming this to the binance-chain/javascript-sdk.

Every hour the query offsets are printed. Binance Chain uses a different swap querying strategy and this monitoring allows for debugging and future optimization:

[2020-06-15T08:54:12.153Z] Current Binance Chain offsets:
[2020-06-15T08:54:12.154Z]      Offset incoming: 0
[2020-06-15T08:54:12.154Z]      Offset outgoing: 0

[denalimarsh]

NOTE: This PR updates @kava-labs/javascript-sdk to ^2.0.0-beta.6, which includes significant client changes. Before this PR is merged all other kava-tools should be run on this branch to confirm everything works fine.

[nddeluca]

I think there is just that one missing return statement is all that needs to be changed.

Rest of feedback is just comments and code style stuff.

[nddeluca]

💯