Add "Omit norms" text datatype.

Problem/Motivation

The schema files provide an entry to use "Omit norms" on text fields by using the to prefix.

    <!-- These text fields omit norms - useful for extracted text like taxonomy_names -->
    <dynamicField name="tos_*" type="text"    indexed="true"  stored="true" multiValued="false" termVectors="true" omitNorms="true"/>
    <dynamicField name="tom_*" type="text"    indexed="true"  stored="true" multiValued="true" termVectors="true" omitNorms="true"/>

However there isn't a datatype to actually expose fields to use this prefix.

Proposed resolution

Add a new SearchApiDataType to add this prefix.

Remaining tasks

User interface changes

API changes

Data model changes