forms: Add free text field

This is similar to the section break but doesn't have the <hr> element
before it and allows for HTML input (including images)
Add concept of client-only form fields
forms: Revisit several small issues for "info" field

  * Use the title of "Information" with internal tag of "info"
  * Add "Visibility" column to UI and retire "Required" and "Internal"
    columns
  * Add visibility selection to new fields and show visibility to the user
    information fields when displayed on the ticket details form
  * Make the visibility settings translatable
  * Use constants internally for visibility configuration detection
  * Use a larger input when managing the information HTML content
  * Fix validation errors for new fields
    * Enforce new field name uniqueness
    * Enforce new field name character validation
forms: Add help tip for new Visibility column
Merge pull request #1329 from greezybacon/feature/field-free-text

forms: Add free text field

Reviewed-By: Peter Rotich <peter@osticket.com>