refs #7666
Using `urlFor('home')` instead `config.get('url')` in Ghost.
When `urlFor('home', true)` returns the absolute adress of the blog as defined in the config.
Will always return a trailing `/`.
closes#7212
When no Blog title is set and there is a `from` mail adress without custom name set up in `config.js`, it will overwrite `config.theme.title` in `GhostMailer.from` and forces to have a (wrong) Blog title after sending a test mail or an invitation.
- Uses a variable `defaultBlogTitle` instead of overwriting `config.theme.title`, when no blog title is set and therefore `config.theme.title` has no value.
