Get module settings now has a $module parameter

## Simplified getting module settings

Instead of:
```
// define mailmotor settings
$settings = BackendModel::getModuleSettings();
$settings = $settings['mailmotor'];
```

We can now use:
```
// define mailmotor settings
$settings = BackendModel::getModuleSettings('mailmotor');
```

The parameter $module is optional, so you still can get all settings by doing:
```
$allSettings = BackendModel::getModuleSettings();
```

## Also updated in core modules

* Mailmotor
* Location