Feature/task permissions

Adds the `filesystem\permissions` to allow change of permissions on given paths. Usage could be :

```yaml
  on-deploy:
    - filesystem/permissions: {paths: application/cache:application/logs, checkPathsExist: true, owner: www-data, group: www-data, rights: 775}
```

Also adds the task `filesystem\permissions-writable-by-apache` wich extends `filesystem\permissions` with default values in order to give Apache user rights to write on given paths. Usage could be :

```yaml
  on-deploy:
    - filesystem/permissions-writable-by-apache: {paths: application/cache:application/logs, checkPathsExist: true}
```