Pocketmine-mp: Button is not solid block

[gistrec]

There is no function 'isSolid()' in button class
And when Player stay near button, it causes damage

Solution: add function 'isSolid()' in StoneButton.php && WoodenButton.php:

```php
public function isSolid(){
return false;
}

[dktapps]

181

I'm not messing with crap I'm going to rewrite. If you want to make a PR to fix this yourself, feel free.