update setupCurrentBlog logic

- move logic to display NewAccount activity to setupCurrentBlog
- handle case where lastBlogId is set, but unable to be set as the
  current blog for whatever reason (maybe the ID no longer exists?). In
  that case, we fall back to just setting the first blog as current
- call setupCurrentBlog during onResume.  This is mainly to handle first
  launch issues where no blog has ever been configured.

git-svn-id: https://android.svn.wordpress.org/trunk@929 a6565c4b-a94d-4d28-bb26-aa9e5ab542c0