Add custom options for seed mixes

[HenriKajasilta]

Description:
There are at least a couple of frequently used seed mixes: Valio's carbo seed mix and Juuso's seed mix. These mixes can include 10 different species and it is not efficient for users to add them manually.

Proposed solution:
Make these seed mixes available in the dropdown menu (sowing - planted crop).

Notes:

• This might require some inquiries about the available mixes.
• On a different note, the seeds are given as kg/ha, but should there be a possibility to give the total amount of seeds (kg) and area of the field (ha) instead?

Images: