Add multiple fields via $fields_form_override

This patch allows multiple fields to be added using the "$fields_form_override" property. Currently, only one field can be added as the array is pushed to the "fields_form" list as a new single field. We have to merge it instead.
[-] FO : Fix big on invalid gift message

Bug not found in forge :
While submitting an invalide gift message (including per example "<" character), processCarrier function attempts to include footer.php (which does not exist anymore ?) and then exits script, instead of letting the classic validate system running and showing an error.
// Themes default column if page not exists
// missing meta pages
// IN : add ignore if meta alreeady in base
//tinymce : plugins added
[*] MO : typos in themeconfigurator module.
[*] BO : typo in AdminCurrenciesController.
//tinymce : plugins removed
Merge branch '1.6' of https://github.com/PrestaShop/PrestaShop into 1.6
Merge branch '1.6' of https://github.com/PrestaShop/PrestaShop into 1.6
[*] BO : better wording for AdminCustomersController.
[~] BO : AdminScenesController : generate images

Generate images in all formats when scenes are saved (when images are uploaded).
// small fix
//small fix on pdf generate
//theme column detection fix
// errors during upgrade to 1.6.0.3
Merge pull request #1365 from axome/1.6

[~] BO : AdminScenesController : generate images
Merge pull request #1364 from xBorderie/patch-3

[*] BO : better wording for AdminCustomersController.
Merge pull request #1363 from xBorderie/patch-2

[*] BO : typo in AdminCurrenciesController.