Fix indexable

I discovered a bug in the `indexable` TableScreen where if you didn't specify your own `table_data_index` method it would display on the screen, but when tapping the index, the application would crash. Unfortunately this is not testable. :(

So I fixed it, added a test to make sure that searchable AND indexable indexes are doing the correct thing, and it should be good to go.

`226 specifications (391 requirements), 0 failures, 0 errors`

Should close #287