add support for multiple subcases in same repeat

This is useful if you want to have a repeat that is as follows:

* What kind of subcase would you like to open
* questions specific to that case type

And case config like

* if "What kind of subcase would you like to open" is "foo" then open into module Foo

* if "What kind of subcase would you like to open" is "bar" then open into module Bar

Each of those case types will have different configuration and so the case block will need to be stored at separate paths. I chose to continue the `subcase_0`, `subcase_1`, etc convention.