Added "name" field under the UUID, containing the last known name of the player.

When a player login, it create a name field just under his UUID in PermBukkit's config.yml. This aim to make easier the reading/editing of the configuration file.

Example :
```yaml
  fa7e312f-7cd1-47de-8570-2b61e124b1c1:
    name: lorgan17
    groups:
    - admin
```