Migrate tags to act_as_taggable_on

This will add missing columns/index
And update datas to macth this new gem. It will add a tagging contaxt of
tags and update the tag counter cache
Migrate game box image over new paperclip storage scheme

You'll need to run

```
$ rake paperclip:move_attachments
```
Start migrating controller/view of public site part

Make index for games/authors/editors
Lots of thing are missing at this time
FIX first letters in game
Update render_widget call and improve a little bit Game#show