Change seed file with a bip39 mnemonic (#207)

* Change seed file with a bip39 mnemonic

* Create helper for bip39 mnemonic

* Prod mode on lamassu-update-to-mnemonic script

* Fix standard styling issues

lib/mnemonic-helpers.js

@@ -0,0 +1,19 @@
+const bip39 = require('bip39')
+const os = require('os')
+
+function fromSeed (seed) {
+  const words = bip39.entropyToMnemonic(seed).split(' ')
+
+  let mnemonic = ''
+  for (let i = 0; i < words.length; i += 6) {
+    mnemonic += words.slice(i, i + 6).join(' ') + os.EOL
+  }
+  return mnemonic
+}
+
+function toEntropyBuffer (mnemonic) {
+  const hex = bip39.mnemonicToEntropy(mnemonic.split('\n').join(' ').trim())
+  return Buffer.from(hex.trim(), 'hex')
+}
+
+module.exports = { toEntropyBuffer, fromSeed }