Move EPM->template->(device)->buttons assignment from global to phone

When setting up the templates for a device we have to create a template for every phone under EPM-brand. You can add multiple devices under the brand but only configure 1 of each type. I am suggesting that when you add a brand, and then create a template for a device we should be able to create a different button layout per phone. The solution right now is to create anew template per extension even though everything in the template is the same except for the button layout (i.e. BLF, call park, etc...) This should ether be moved to the extensions (i.e. click on an extension in EPM->extensions mapping, or the extensions module (when you click on the template and model), or allow us to create an array of templates when in a specific template and we click on the device.

For example. in EPM-Brand I create Grandstream. Now in EPM->Brand->Grandstream I create a template for a model like GXP2170 (called GXP2170). When I go into EPM-Grandstream->GXP2170 I should be able to add multiple button templates (and name them, or choose an existing extension with this type device) and then assign the button layout. 

Ass an added feature allow us to copy the button layout from another extension of the same type since in many cases the layout may be very similar for several phoens