add layer name filtering from R side

[MilesMcBain]

What we want from this control is that you can either select entire groups or ungrouped layers.

At the moment the layers tidyselect will also select grouped layers, but these will be ignored by rdeck because they will be passed with groupName = null. This probably relies a little too heavily on rdeck implementation details.

Name layers that are in groups should not be selectable from the R side, and should not be passed into web world as data.