PDP Package.layout implementation

[aaronjudd]

The goal of this feature is to allow repositioning (layout) of functional blocks on the PDP page, as well as the addition, removal and permission based viewing of blocks as necessary.

We'll need to refactor the Product Detail Page to use ReactionTemplates, using Packages.layout entries to define different product types and associate layout and templates with the PDP based on the product's Product.type entry.

This will make the PDP less rigid, and makes implementation much simpler for #152, #343, #330, #191, #368, #367, #443, #500, #516 , #225.

ProductDetail.html will become a layout loader page, essentially just:

{{#each reactionTemplate provides=product.type}}
    {{> Template.dynamic template=template}}
{{/each}}

and we add a new layout entry in register.js for the simple PDP layout:

 {
    template: "simpleProduct",
    label: "Simple Product",
    provides: "simple",
    audience: ["guest", "anonymous"]
  }

assuming type = simple, and where we've created a new product layout template:

<template name="simpleProduct">
  ...
  <div class="col-sm-7 pdp-right-column">
    {{#each reactionTemplate provides=product.type container="pdp-right-column"}}
        <div class="row">
            {{> Template.dynamic template=template}}
        </div>
    {{/each}}
    </div>
...
<template>

the individual blocks get moved into their own templates:

<template name="productDescription">
   <div class="product-description">
     {{> fieldComponent field="description" value=description type="textarea"}}
   </div>
</template>

The register.js will get a new layout entry for each PDP template:

 {
    template: "productDescription",
    label: "Description",
    container: "pdp-right-column",
    audience: ["guest", "anonymous"],
    position: "2"
  }

[aaronjudd]

@mikemurray have you considered this during your updates.. let's discuss...