Fixed warnings on startup

For a while now we've had some warnings during the start-up phase that annoyed me.
This PR fixes the following:
* Not logging error during swagger recursion when /lib does not exist (as it is legal)
* Specifying widget directory filter for caching widget manifests/i18n bundles

These still remain:
```
[2014-09-20T17:46:23.192Z]  WARN: signature/33164 on dhcp-172-17-169-188.eduroam.wireless.private.cam.ac.uk:
    You are using the default key to sign URLs, this is *NOT* secure and should be changed immediately.
    The system will continue to function, but it is strongly recommended that you change your key.
[2014-09-20T17:46:24.646Z]  WARN: mq/33164 on dhcp-172-17-169-188.eduroam.wireless.private.cam.ac.uk:  (queueName=oae-preview-processor/generatePreviews)
    Error: Attempted to unbind listener from non-existant job queue. Ignoring
        at EventEmitter.module.exports.unsubscribeQueue (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/mq.js:508:52)
        at Object.module.exports.unbind (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/taskqueue.js:132:8)
        at module.exports.disable (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/api.js:110:15)
        at EventEmitter.module.exports.refreshPreviewConfiguration (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/api.js:153:5)
        at module.exports (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/init.js:42:16)
        at initModule (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/modules.js:82:46)
        at /Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/modules.js:88:21
        at _createColumnFamilies (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/cassandra.js:330:16)
        at /Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/cassandra.js:338:9
        at /Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/cassandra.js:299:13
[2014-09-20T17:46:24.646Z]  INFO: oae-preview-processor/33164 on dhcp-172-17-169-188.eduroam.wireless.private.cam.ac.uk: Unbound the preview processor from the generate previews task queue.
[2014-09-20T17:46:24.647Z]  WARN: mq/33164 on dhcp-172-17-169-188.eduroam.wireless.private.cam.ac.uk:  (queueName=oae-preview-processor/regeneratePreviews)
    Error: Attempted to unbind listener from non-existant job queue. Ignoring
        at EventEmitter.module.exports.unsubscribeQueue (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/mq.js:508:52)
        at Object.module.exports.unbind (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/taskqueue.js:132:8)
        at /Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/api.js:119:19
        at EventEmitter.module.exports.unsubscribeQueue (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/mq.js:509:16)
        at Object.module.exports.unbind (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/taskqueue.js:132:8)
        at module.exports.disable (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/api.js:110:15)
        at EventEmitter.module.exports.refreshPreviewConfiguration (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/api.js:153:5)
        at module.exports (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-preview-processor/lib/init.js:42:16)
        at initModule (/Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/modules.js:82:46)
        at /Users/sg555/projects/apereo/oae/Hilary/node_modules/oae-util/lib/modules.js:88:21
```


The first one should stay as it's pretty important. We could do the other ones when we remove the REST coupling from the preview processor.