Suggestions

[hvianna]

First of all, I'm sorry for my PR completely without notice. I'm new to contributing code here on GitHub and still learning the ropes (plus, poor social skills).. Anyway, I have a few more suggestions that were just commited and I just realized they would be included in the original PR, so I decided to open this issue and properly present my suggestions.

So here's a summary of changes proposed in #19

• wp_get_sites() is deprecated since 4.6, so it was replaced by get_sites();
• Category fields are now also displayed in the super-admin add site form (I suppose many networks won't allow users to create new sites themselves);
• Added action/function to load the plugin's textdomain for translations;
• Added pt_BR translation;
• Renamed previous translation files to match the textdomain (I haven't updated the strings though);
• Added action/function to redirect single site posts to the actual
  sites in the network (works great for search results on your network main site);
• Renamed the admin menu item from 'Sites' to 'Directory', so it won't
  get confused with the network admin menu item.

[fabacab]

Thank you so much for the pull request. You're 💯% awesome!

For what it's worth, it's perfectly okay with me if you open a pull request instead of an issue. I use issues as a sort of "to do list" while pull requests are more useful to me as a showcase of work in progress. Pull requests are also more appropriate in this case than a single issue is because a pull request can contain more than one chunk of behavior (as long as the commits in the pull request are atomic), whereas issues that represent more than one distinct issue undermines the utility of using an issue tracker in the first place. ;)

So, with that said, I really like your suggestions and will review them in the pull request itself.