Add fermentables support

[drodil]

To be able to do more calculations add information about most known fermentables to the application. There should be at least the following information available:

• Name
• Country (if applicable)
• Category (grain/fruit/adjunct/sugar/liquid extract/dry extract)
• Type (base malt/roasted malt/specialty malt/crystal malt/gluten-free malt/raw/fruit/juice/extract)
• Color (°L)
• PPG
• Potential
• Yield

Add the most used fermentables as constants (see #23 as an example) and command to find fermentables based on criteria. Also see #43 if it can bring any help to this.

For potential and yield you can find some information here https://www.homebrewtalk.com/wiki/index.php/Malts_Chart