Attempt to add support for clims to plotly backend

Added support for clims, seems to work on heatmap, surface and contour.
On surface zlims be still be set to be different from clims.

src/backends/plotly.jl

@@ -31,6 +31,7 @@ const _plotly_attr = merge_with_base_supported([
     :hover,
     :inset_subplots,
     :bar_width,
+    :clims,
   ])
 
 const _plotly_seriestype = [
@@ -438,6 +439,11 @@ function plotly_series(plt::Plot, series::Series)
         end
     end
 
+    clims = sp[:clims]
+    if is_2tuple(clims)
+        d_out[:zmin], d_out[:zmax] = clims
+    end
+
     # set the "type"
     if st in (:path, :scatter, :scattergl)
         d_out[:type] = st==:scattergl ? "scattergl" : "scatter"