Use callback in placeSeedWord method.

When displaying seed words, we were not using a callback, which had some race condition potential.  This is simply a little cleaner and more correct.

Fixes #842

app/scripts/keyring-controller.js

@@ -173,10 +173,15 @@ module.exports = class KeyringController extends EventEmitter {
     })
   }
 
-  placeSeedWords () {
+  placeSeedWords (cb) {
     const firstKeyring = this.keyrings[0]
     const seedWords = firstKeyring.serialize().mnemonic
     this.configManager.setSeedWords(seedWords)
+
+    if (cb && typeof cb === 'function') {
+      cb()
+      this.emit('update')
+    }
   }
 
   submitPassword (password, cb) {

ui/app/actions.js

@@ -221,9 +221,11 @@ function requestRevealSeed (password) {
   return (dispatch) => {
     dispatch(actions.showLoadingIndication())
     background.submitPassword(password, (err) => {
-      dispatch(actions.hideLoadingIndication())
       if (err) return dispatch(actions.displayWarning(err.message))
-      background.placeSeedWords()
+      background.placeSeedWords((err) => {
+        if (err) return dispatch(actions.displayWarning(err.message))
+        dispatch(actions.hideLoadingIndication())
+      })
     })
   }
 }