Support finding children in ListView & GridView

[LubosD]

This PR also contains changes from #2, otherwise you'd have a merge conflict.

[faaxm]

Could you add a basic example to Spix that shows its usage with ListView & GridView? It could be something really basic (like query the .text property of an item in the views and print it to the ResultView from the basic example)?

I hope to eventually run the examples that come with Spix on the build server and use them as smoketests. Especially to test Spix against different versions of Qt, so it would be great if all main features are somewhat represented in the examples.

[faaxm]

Thank you for looking into this. While adding examples, I realised that itemAtIndex(...) is only supported by ListViews in Qt 5.13 or later. I decided to look for an alternate implementation and implemented one in commit be430a9
Could you have a look if this also works for your usecase?

As a bonus, with these changes, it is no longer required to explicitly mention the repeater/listView/gridView object in the ItemPath.