In List and List's inherited tiles, we should check if an object is a container and get info from it's image

[idgserpro]

For example: in carousel tile, which inherits ListTile, we have a get_alt method:

return obj.Description() or obj.Title()

The problem with this approach is that if you're using for example a collective.nitf.content which is a container and can have an image, you don't get information about the image itself: this way we don't have an alt attribute and an acessibility problem:

A similar behavior happens in collection tiles (https://github.com/collective/collective.cover/blob/1.8b2/src/collective/cover/tiles/collection.py#L222).

Since both List and Collection inherit from PersistentCoverTile, I suggest moving get_alt to PersistentCoverTile, and have a different approach. Something in the lines of:

https://github.com/plonegovbr/brasil.gov.tiles/blob/1.x/src/brasil/gov/tiles/tiles/collection.py#L202

The comments are in Portuguese, but the code is self explanatory.

[hvelarde]

IMO this is related to #778.