Filter Extension

[SymbolixAU]

https://github.com/uber/deck.gl/blob/37b5841ccefc3541b57ac33ae4b21ec0c4700fda/docs/extensions/data-filter-extension.md

Design ideas:

• Extensions can be used by multiple layers (with some limitations, like data filter).
• Need a way to optionally add the extension properties to the constructor of each layer.
• Also need to hook up the extensions with input controls,

[dcooley]

related - https://github.com/SymbolixAU/spatialwidget/issues/42

lapply( other_columns, function(x) {
  l[[x]] <<- x
})

l[["other_columns"]] <- NULL