Use identifier to store utility class selection

Problem/Motivation

Currently, the values of the classes associated with a utility class are defined directly, which could be problematic if in an existing site, you want to change the structure of theming or classes or you want to use another base theme that requires different utilities.

Proposed resolution

1. Add an identifier field to each value of a utility class to store the value of the class selection (instead suffix value that may require adjustments), also use that value as saved value instead the current one.
2. Add description to "Identifier" fields in form to inform that changing that value produce any utility usement loss (to both fields, utility & new for each value).
3. Avoid any related regression to current installation sites (update or TBD).