[ANN] ba-st Web stack updated (RenoirSt, Willow and HighchartsSt)

Now that Pharo 7 is finally released, we took some time to update the whole web stack hosted at ba-st.

As a general update all the projects now follow the brand new community guidelines and support Pharo 6.1–32 bits and Pharo 7–32 & 64 bits. The build matrix now includes Pharo 8 as a preview.