Suport multiple apps syndication

[SalahAdDin]

• Python 3.6.4.
• Django 2.0.1.
• Wagtail 2.0b1.
• Chrome 64.

Currently we only can use a single app for syndication, but users can to want create syndication feeds for multiple apps: news, blogs, etc., for example.

What's about this?

[chrisdev]

@SalahAdDin @Parbhat since all page "types" for example BlogPage, StandardPage, Event etc are subclasses of Page we should be able to support this. So that user gives us is a list of models they wish to include in the Feed (and the associated date ordering field) We do a query based on the Pages model to give us the items. I don't know It sounded crazy when I thought of doing it this way but I think it just could work? What do you think @SalahAdDin @Parbhat ?

[SalahAdDin]

@chrisdev It's actually my idea. We can use some like InlinePanel for add each new field, i think.

[chrisdev]

@SalahAdDin yes this is a great idea 👯‍♂️ . I will really take the package up to the next level of useful.
So can we expect a PR?

[SalahAdDin]

I don't know how can we begins this feature but i can contribute to a existing PR. :(

Ok, give me a minute, i'm thinking about it.

[SalahAdDin]

#43
Here is my effort. :'(

[SalahAdDin]

@chrisdev, i want to discuss wich is the best approach for do this: i'm thinking to create a FeedApp for each app to blog, but, i'm not sure if it would better fix some fields as a global option and just left a few fields as dynamic per app.

What do you think?