Improve search placeholder text.

[allanchau]

Expected behaviour

We should be able to customise the search placeholder text.

Actual behaviour

The text is set to the model name.

Notes

I think list.search should be updated to be an object that accepts fields and placeholder properties. The placeholder text would override the default if provided.

The default placeholder text should also be updated to list the labels of the search fields instead of the model name since the model title is already next to the search bar? eg Search ${label}, ${label2}, and ${label3}. This would prevent any confusion on what the user can search for.