add 'CakeResque.Status.lib' config option

It's already done correctly for the 'php-resque-ex' and 'php-resque-ex-scheduler' packages. I've just added the ability to specify a path to the 'resque-status' package via the configs, so it's consistent with the other two.

The reason I need it is because I'm using Composer to install the Cake-Resque plugin itself - not just its dependencies. So, Composer installs ALL dependent packages in /Vendors - not in the `CakePlugin::path('CakeResque') . 'vendor' . DS;` directory. So, I need to be able to specify the correct path to that via a config option.

You'll see in my comments that I've done a work around so as not to break things for existing users, but really I think this config option should probably be required in the next major version.

Also, on another note, I think the `$pluginVendorPath` itself should probably be configurable for the same reason - people using composer may have different vendor paths. However, I I haven't changed that in this PR.

FYI, my own custom bootstrap file looks like this:

```
$vendorPaths = App::path('Vendor');
$appVendorPath = $vendorPaths[0];
Configure::write('CakeResque.Resque.lib', $appVendorPath . 'kamisama' . DS . 'php-resque-ex');
Configure::write('CakeResque.Scheduler.lib', $appVendorPath . 'kamisama' . DS . 'php-resque-ex-scheduler');
Configure::write('CakeResque.Status.lib', $appVendorPath . 'kamisama' . DS . 'resque-status' );
```

Since I'm having composer install them with the exact same name but just at a different location, if there was a config option for the $pluginVendorPath then all I'd need to do is this:

```
$vendorPaths = App::path('Vendor');
$appVendorPath = $vendorPaths[0];
Configure::write('CakeResque.PluginVendorPath', $appVendorPath);
```
(of course, anyone using Composer to install their Cake plugins is in the same situation)

Signed-off-by: Joshua Paling <joshua.paling@gmail.com>