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
* etc.

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.