Adding validations for meta_* fields to match Database-constraints.

This fixes #5514. When using MySQL and inserting text into a string
field, the database will flunk if you commit over 255 characters.
This patch adds a few validations to make sure the various
meta_*-fields, using strings in the database, will contraint the lenght
with a maximum of 255 characters.

Fixes #5514
Fixes #5516
create the partial for the promotion sub menu

remove duplicate buttons

This was the main reason for the PR. The preceding commits basically
set up the tab and render it, but this commit shows how much code gets
to be deleted and how much smoother and the promotions tab becomes :D

fixes #5517