Alan D.'s sandbox: Taxonomy term (with other support)

Alternative to the Select (or other)'s Term widget.

Objectives & differences

• Supports multiple vocab sources
• Grouping option if multiple vocabs used for select lists. Core patch required. ^*
• Stores both the term ID and value in the database.
• Widget settings switch between standard Option widgets (select list, radios or checkboxes) or the Select or other version
• No auto-create for terms nor updating field settings
• Std term formatter uses the plain text or linked term title options, with either std list or inline options

When using the Other option (Select or other is a dependency for this feature)

• Automatically remembers deleted terms

^* Group option requires a core patch
#1180992: [D8] list_field_validate() doesn't seem to accommodate select lists with <optgroup>
No patch for Drupal 7, just a single line mod.

modules/field/modules/list/list.module, line 391
-  $allowed_values = list_allowed_values($field, $instance, $entity_type, $entity);
+  $allowed_values = options_array_flatten(list_allowed_values($field, $instance, $entity_type, $entity));