Fix OAI filter for requiring public ORIGINAL bitstream

While trying to enable the bitstreamaccessFilter in XOAI.xml, I encountered some issues.

oai.storage = database, the `DSpaceSetSpecFilter` was failing to grab the handle correctly from the request, needed to convert 123456789_2309 to 123456789/2309.

Also, my interpretation of full-text available for an item is that there is a Bitstream in the ORIGINAL bundle, that is publicly readable. The DB version of that `DSpaceAuthorizationFilter` was correct, but the SOLR version was too loose, and only required that the item be publicly accessible. To fix that, I added a new boolean field to the oai solr schema: `item.publicBitstream`. You'll need to reindex for this to work correctly.

Lastly, to enable to the `bitstreamaccessFilter` for any DSpace instance, ensure that their `dspace/config/crosswalks/oai/xoai.xml` has something like this:
```
<Context baseurl="request">
    <Filter refid="bitstreamaccessFilter"/>
    ...
```