Update viz layer examples

[makella]

PR to update some examples with new features.

• range_min and range_max for color/size continuous layers
  • Update color and size continuous viz layer examples #1143
• Add example for isoline_layer helper
  • add example for isoline viz layer helper #1144

[makella]

@Jesus89 please review!

as mentioned above, this PR does some updates to the Visualization Layer examples:

• adds the range_min and range_max parameters to the color/size continuous layer examples - - adds an isoline layer example
• adds the isoline layer to examples.json

why oh why do I fail again! :/

thanks!!

[Jesus89]

LGTM!

Note: I'm not sure about adding a widget to select the range in the isolines_layer example, because the user can select one "ring" but this is implemented just to render all the ranges together.

[makella]

good point! i thought the same thing... should we remove widget=true from the example then?