BK-1322 Create default roles for Booktype project

I have created a management command for creating|updating  default roles for the system. This command depends on new settings variable called BOOKTYPE_DEFAULT_ROLES. Also now we have validations for reader app (full view and draft page). We probably gonna need to add more validations.

In book settings screen, I have added an option to define the default role for anonymous and registered user in current book. 

In control center, we can override the default roles for the ones we want.

That's about it