Add the `$idPrefix` config option to FormHelper
Add the `$idPrefix` config option to FormHelper

closes #6134
CVO-Technologies/cakephp,bravo-kernel/cakephp,erikfig/cakephp,mvdriel/cakephp,pbaire/cakephp,tenkoma/cakephp,elboletaire/cakephp,elboletaire/cakephp,cakephp-fr/cakephp,davidyell/cakephp,adopico/cakephp,michaelze/cakephp,timhoeppner/cakephp,pbaire/cakephp,cakephp/cakephp,mvdriel/cakephp,cakephp-fr/cakephp,tenkoma/cakephp,pbaire/cakephp,kumamidori/cakephp,bravo-kernel/cakephp,jjj117/cakephp,eryw/cakephp,burriko/cakephp,khoimt/cakephp-study,Balachan27/cakephp,Balachan27/cakephp,yinhe007/cakephp,yinhe007/cakephp,dkarvounaris/cakephp,berrygoudswaard/cakephp,nrother/cakephp,CVO-Technologies/cakephp,thinkingmedia/cakephp,erikfig/cakephp,tgr0ss/cakephp,ionas/cakephp,mvdriel/cakephp,gmponos/cakephp,web-player/cakephp,erikfig/cakephp,HavokInspiration/cakephp,ndm2/cakephp,justinyost/cakephp,tenkoma/cakephp,CVO-Technologies/cakephp,web-player/cakephp,gmponos/cakephp,nrother/cakephp,garethellis36/cakephp,ADmad/cakephp,garethellis36/cakephp,dakota/cakephp,nrother/cakephp,ADmad/cakephp,eryw/cakephp,petteyg/cakephp,adopico/cakephp,akintoey/cakephp,CakeDC/cakephp,eryw/cakephp,CakeDC/cakephp,tisu2tisu/cakephp,gmponos/cakephp,dkarvounaris/cakephp,eboominathan/cakephp,justinyost/cakephp,ADmad/cakephp,elboletaire/cakephp,CakeDC/cakephp,Balachan27/cakephp,garethellis36/cakephp,dakota/cakephp,jerems02/cakephp,akintoey/cakephp,tenkoma/cakephp,dakota/cakephp,ionas/cakephp,burriko/cakephp,ionas/cakephp,jjj117/cakephp,garethellis36/cakephp,justinyost/cakephp,Phillaf/cakephp,berrygoudswaard/cakephp,timhoeppner/cakephp,dakota/cakephp,jerems02/cakephp,web-player/cakephp,cakephp/cakephp,cakephp/cakephp,petteyg/cakephp,HavokInspiration/cakephp,petteyg/cakephp,tgr0ss/cakephp,ndm2/cakephp,akintoey/cakephp,petteyg/cakephp,tgr0ss/cakephp,yinhe007/cakephp,ndm2/cakephp,HavokInspiration/cakephp,michaelze/cakephp,dkarvounaris/cakephp,Phillaf/cakephp,cakephp/cakephp,cakephp-fr/cakephp,khoimt/cakephp-study,jeffblack360/cakephp,thinkingmedia/cakephp,davidyell/cakephp,timhoeppner/cakephp,tisu2tisu/cakephp,ndm2/cakephp,khoimt/cakephp-study,ADmad/cakephp,thinkingmedia/cakephp,berrygoudswaard/cakephp,Phillaf/cakephp,kumamidori/cakephp,davidyell/cakephp,bravo-kernel/cakephp,jeffblack360/cakephp,burriko/cakephp,CakeDC/cakephp,jerems02/cakephp,mvdriel/cakephp,jeffblack360/cakephp,adopico/cakephp,eboominathan/cakephp,eboominathan/cakephp,jjj117/cakephp,kumamidori/cakephp,michaelze/cakephp,tisu2tisu/cakephp