Request: Give the BlocklyProp environment the ability to have different color schemes

[francisbauer]

The ability to change the BlocklyProp color scheme is a desirable feature. While experimenting with BlocklyProp recently, my wife (who is also a multi-lingual/environment programmer) commented that the current BlocklyProp color scheme is a bit too harsh to be sitting in front-of for long periods of time. Color schemes are always subjective and every user has their preferences. Giving BlocklyProp the ability to have even a limited set of Color schemes would go a long way to pleasing a wider audience. Documentation could still use the default Color scheme for consistancy, which is what other environments do.