[*] BO : Fixes issue with not beeing able to edit weight beacuse string is longer then max length

This is more of a suggestion...

If i set weight to 0.700 on a product, and then save it. It will be changed to 0.700000 by the mysql.
And then if enter the product again, and delete the 7 and then type an 8, I can't, because the string exceeds maxlength of 6. I have to delete some zero's to able to set my new weight.
The length 21 i took from the fact that weight and so on can contain a total of 20 decimals. So 20 decimals + 1 . = 21.