Coded value map index normalizer

Coded value map index normalizer

New index normalizer which maps a coded value from the record to the
display value configured in config.coded_value_map.  The normalizer is
applied with one parameter, the ctype of the coded_value_map to use for
the mapping.

E.g config.metabib_field_index_norm_map:

id | field | norm |    params     | pos
---+-------+------+---------------+-----
57 |    31 |   17 | ["item_lang"] |  -1

* pos = -1 causes this normalizer to be applied to facet_entry's

This is primarily useful for facets.  For example, you could create a
metabib_field for language and mark it as a facet_field.  Applying this
index would allow the mapped language names (e.g. "French" instead of
"fre") to display as facets.

Signed-off-by: Bill Erickson <berick@esilibrary.com>