ggplot: scatterplot: hollow circles, symbol mappings, marker style

ggplot: scatterplot: hollow cicles

- `shape=1` in ggplot is `circle-open` in Plotly

Example: 
```
sampledat <- diamonds[sample(nrow(diamonds), 500), ]
p <- ggplot(data = sampledat, aes(carat, price, colour = cut)) + 
  geom_point(size = 5, alpha = 0.5, shape = 1) +
  labs(title = "Scatter Plot Example", x = "Carat", y = "Price", colour = "Cut") 
```
https://plot.ly/~pdespouy/1593/scatter-plot-example/

cc/ @mkcor @chriddyp