Create serializers on demand

[diegocastrum]

There are situations where applications make use of preferences, settings and/or options storing them into different JSONFields across the application. In this cases it would be useful if we can map those options properly defined in a data structure or a collection to Serializers that will be created on demand.

With this approach we could have all those kind of options defined in a central place instead to have to maintain all serializers separately dispersed in different modules.

Next to this, options, preferences and those kind of settings tend to grow up over time, so having them all defined in a central place could improve the management of those options.

If this approach is interesting and could be implemented in django-rest-framework I could work on it, I already have implemented something like this from scratch in other project and seems to work as desired.