global: /record configurable via CFG_SITE_RECORD
- Creates config option CFG_SITE_RECORD that represents '/record' part of detailed record pages URI, so that Invenio sites can set this natively to have some other value such as '/abs' in place of `/record'.
- Changes all files that reference hardcoded /record in order to use CFG_SITE_RECORD. (Web tests weren't changed.)