Add color calculator

[drodil]

To be able to calculate SRM we need the fermentable information with color as well as batch size and amount of fermentable. See #44 for support of basic fermentables so the user does not need to input the color information for every fermentable. The formula for this can be found in http://beersmith.com/blog/2008/04/29/beer-color-understanding-srm-lovibond-and-ebc/

Additionally the calculator should give out SRM (Standard Reference Method), Degrees Lovibond and EBC (European Beer Color) and hex value for the color. See https://www.brewersfriend.com/color-calculator/ as an example of the conversion. The conversion should be placed in another calculator so that it can be used as its own command.