Enumeration fields should allow multiple values

A field of type `enumeration` should allow the selection of multiple values at once.
The back-end supports multiple tags for an entry.
The UI selector allows choosing only one value from the UI.

**Expected**
1. Given a table with a column of type `enumeration` with multiple available choices
2. Add/edit a row in said table
3. A user can select one or more values

**Actual**
1. Given a table with a column of type `enumeration` with multiple available choices
2. Add/edit a row in said table
3. Only one of the available choices can be set

**Suggestion**
The widget used when creating a field of type `enumeration` may also be helpful in this situation.