Renamed getWrapped* functions

Considering (C) in #59 

I made some changes that IMHO makes the `BaseSpecification` easier to understand. Compare code examples from #59. 

``` php
class PowerUser extends BaseSpecification
{
    /**
     * @return Expression
     */
    protected function initExpression()
    {
        return Spec::andX(
            Spec::eq('test', 2),
            Spec::gt('length', 4, 'c')
        );
    }

    /**
     * @return Modifier
     */
    public function initQueryModifier()
    {
        return new ModifierCollection(
            Spec::join('comments', 'c'),
            new OrderBy('name')
        );
    }
}
```

``` php
class AnyUser extends BaseSpecification
{
    function __construct($limit, $dqlAlias=null)
    {
        parent::__construct($dqlAlias);
        $this->spec = Spec::orX(new PowerUser(), new OtherUser());
        $this->limit = $limit;
    }

    /**
     * @return Modifier
     */
    public function getWrappedModifier()
    {
        return new ModifierCollection(new Limit($this->limit), $this->spec);
    }
}
```

```php

class SomeService
{
  public function foo()
  {
    $users=$this->repo->match(new AnyUser(5), new ModifierCollection(new AsArray(), new SomethingElse());
  }
}

```

``` php
class LazyUser extends BaseSpecification
{
    function __construct($limit, $dqlAlias=null)
    {
        parent::__construct($dqlAlias);
        $this->spec = Spec::andX(Spec::Not(new PowerUser()), new SomeSpec());
    }
}
```

``` php
class AnimalSpec extends BaseSpecification
{
    /**
     * @return Expression
     */
    protected function initExpression()
    {
        return Spec::eq('animal', true);
    }
}
```