fix(account-prefs): Update account save logic to prevent incorrect saves

- This fixes #1354 and #1235
- This issue was caused because the account details preferences
  component was keeping as state all of the account object fields. `setState` works
  like `extend`, so when the account changed, state was set to the new set of account fields,
  but the old values were only removed if they were overriden, and remained the
  same if the field did not exist in the new state object.
  Specifically, when a new account was added, setState was called with
  `{..., defaultAlias: undefined}` which did /not/ remove the  the defaultAlias
  from the previous state.
- Switched to managing state with a top level key `account`

internal_packages/preferences/lib/tabs/preferences-account-details.jsx

@@ -12,11 +12,11 @@ class PreferencesAccountDetails extends Component {
 
   constructor(props) {
     super(props);
-    this.state = _.clone(props.account);
+    this.state = {account: _.clone(props.account)};
   }
 
   componentWillReceiveProps(nextProps) {
-    this.setState(_.clone(nextProps.account));
+    this.setState({account: _.clone(nextProps.account)});
   }
 
   componentWillUnmount() {
@@ -51,30 +51,32 @@ class PreferencesAccountDetails extends Component {
     return `${name} <${email}>`;
   }
 
-  _updatedDefaultAlias(originalAlias, newAlias, defaultAlias) {
-    if (originalAlias === defaultAlias) {
-      return newAlias;
-    }
-    return defaultAlias;
-  }
-
   _saveChanges = ()=> {
-    this.props.onAccountUpdated(this.props.account, this.state);
+    this.props.onAccountUpdated(this.props.account, this.state.account);
+  };
+
+  _setState = (updates, callback = ()=>{})=> {
+    const updated = _.extend({}, this.state.account, updates);
+    this.setState({account: updated}, callback);
+  };
+
+  _setStateAndSave = (updates)=> {
+    this._setState(updates, ()=> {
+      this._saveChanges();
+    });
   };
 
 
   // Handlers
 
   _onAccountLabelUpdated = (event)=> {
-    this.setState({label: event.target.value});
+    this._setState({label: event.target.value});
   };
 
   _onAccountAliasCreated = (newAlias)=> {
     const coercedAlias = this._makeAlias(newAlias);
     const aliases = this.state.aliases.concat([coercedAlias]);
-    this.setState({aliases}, ()=> {
-      this._saveChanges();
-    });
+    this._setStateAndSave({aliases})
   };
 
   _onAccountAliasUpdated = (newAlias, alias, idx)=> {
@@ -85,9 +87,7 @@ class PreferencesAccountDetails extends Component {
       defaultAlias = coercedAlias;
     }
     aliases[idx] = coercedAlias;
-    this.setState({aliases, defaultAlias}, ()=> {
-      this._saveChanges();
-    });
+    this._setStateAndSave({aliases, defaultAlias});
   };
 
   _onAccountAliasRemoved = (alias, idx)=> {
@@ -97,16 +97,12 @@ class PreferencesAccountDetails extends Component {
       defaultAlias = null;
     }
     aliases.splice(idx, 1);
-    this.setState({aliases, defaultAlias}, ()=> {
-      this._saveChanges();
-    });
+    this._setStateAndSave({aliases, defaultAlias});
   };
 
   _onDefaultAliasSelected = (event)=> {
     const defaultAlias = event.target.value === 'None' ? null : event.target.value;
-    this.setState({defaultAlias}, ()=> {
-      this._saveChanges();
-    });
+    this._setStateAndSave({defaultAlias});
   };
 
 
@@ -129,7 +125,7 @@ class PreferencesAccountDetails extends Component {
   }
 
   render() {
-    const account = this.state;
+    const {account} = this.state;
     const aliasPlaceholder = this._makeAlias(
       `alias@${account.emailAddress.split('@')[1]}`
     );