fix(onboarding): AccountStore only listens to changes to account obj when window

type is composer

- AccountStore was listening to changes to account object (config file)
when it was a window different from the main window in order to update
the alias list on composer windows.
- This caused the onboarding window to also listen for changes and
caused it to incorrectly add an account twice

src/flux/stores/account-store.coffee

@@ -35,7 +35,7 @@ class AccountStore
       @_load()
       if newAccountIds.length > 0
         Actions.selectAccount(newAccountIds[0])
-    unless NylasEnv.isMainWindow()
+    if NylasEnv.isComposerWindow()
       NylasEnv.config.observe saveObjectsKey, => @_load()
 
     @_setupFastAccountCommands()

src/nylas-env.coffee

@@ -337,6 +337,9 @@ class NylasEnvConstructor extends Model
   isWorkWindow: ->
     @getWindowType() is 'work'
 
+  isComposerWindow: ->
+    @getWindowType() is 'composer'
+
   getWindowType: ->
     @getLoadSettings().windowType