Allow storing extracted fulltext in blobs

Fulltext extracted from binaries can be stored in a blob provider instead of metadata in the repository by defining: nuxeo.vcs.fulltext.storedInBlob= true (Note that despite the vcs in the name, which is here for regularity with other properties, it also applies to DBS/MongoDB.) When doing so, by default a BlobProvider named fulltext will be used to store these blobs. When using a custom blob provider configuration instead of the default local filesystem storage, this fulltext blob provider must be defined accordingly. Usage of this specific blob provider is configured through a blob dispatcher in the default configuration, which may be overridden if needed. When defining additional repositories, fulltext blob storage will need to be enabled with XML in the repository contribution: <fulltext ... storedInBlob= "true" ... /> and a custom blob dispatcher configuration will be needed to take into account this repository. Note that when fulltext blob storage is enabled, repository-based fulltext search is automatically disabled (equivalent to nuxeo.vcs.fulltext.search.disabled=true or <fulltext ... searchDisabled="true" ... /> ).