Add alternative identifiers fields, fixes #6107

- Create partial and component to edit and index the new fields
- Add those partials to ISAD, RAD and DACS templates
- Add JavaScript and CSS to manage the link
- Add new fields in the EAD import/export proccess and in the search index

Squashed commit of the following:

commit f85b65dcadefc013a71f51b05be35afa359d1d27
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Dec 11 06:38:11 2013 +0100

    Add new fields in the search index

commit 6e42bfeb195ec7e9dfc29c50a5e16ef755f715d7
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Dec 11 05:47:20 2013 +0100

    Add EAD import/export

commit 0bc0fac4de4124a5b7d7a83087c0823ec8de12c2
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Dec 11 03:57:55 2013 +0100

    Add alternative identifiers fields

    - Create partials and component to edit and index this fields
    - Add those partials and component to de ISAD, RAD and DACS templates
    - Add js and css to manage the link behaviour