Need to support quantity for addons

[vikasrohit]

As of now, user can not specify the quantity of add-ons when configuring the project. We need to add support to let user choose multiple quantity per add-on and calculate the total price as per the quantity selected by user per addon.

[maxceem]

As now you've implemented pretty much the same what I was thinking about in you commit 79fc9b9#diff-bcfd7970e8edc78f9946daa468a139a5

To be able to define it per add-on we should add ths allowMultiple property to each productTemplate object which represents add-on.

There are several ways to do it, which come to my mind:

1. Add a new allowMultiple property to the productTemplate. This feels like not a good solution as we also use productTemplate model for product templates which don't need this param.
2. Add a new allowMultiple property to the root of JSON inside template property - this sounds like a good and simple solution.
3. We can go feature and generalize add-ons quantity to any set of form fields per add-on.
   The idea is next. Do we use template inside add-ons anywhere? Or are we going to use it?
   If not, we can define a form per add-on inside template and render it for each selected add-on. So for now, such a form inside template would only contain quantity question to select the quantity. But potentially, we could add any form to configure particular add-on as we need. This is just an idea, not sure if it makes sense for our future plans.

[maxceem]

There is some issue in the current implementation, I'm getting error when I use the template https://connect.topcoder-dev.com/new-project/subtitle and trying to choose any add-on.

I've made a quick fix in the next commit eef5e38

[vikasrohit]

Thanks @maxceem for the fix and its good to have that fix in place. However, ideally code should not land into that place because if an addon is selected then only our logic here would filter that addon block and if a block is filtered out, we should be able to find it in addonsData.

[vikasrohit]

Just made one more safe check 644c40a

[vikasrohit]

Done, closing the issue.