Show generic rep. in search results, fixes #4919

Squashed commit of the following:

commit 6d414294f79ba9aaf5de37d174013e3c68b78061
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Sat Jul 13 04:58:15 2013 +0200

    Show generic representation in search index.

    Show generic representation for digital objects
    without thumbnail

commit b2cc6b349ee66f9aca6525b0426a616538bbeb74
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Sat Jul 13 04:55:49 2013 +0200

    Add field in QubitSearchInformationObject.

    Add unindexed mime_type field