Taxation calculator allows users to select more than 12 months

[calvin-zeu]

The new tax calculator allows users to enter more than 12 months, which is not compatible with the German calendar year, which consists of 12 months.
The optimisation tool also automatically assigns 13 or more months to users after a certain number of entries have been made.

Possible solutions could be:

• limiting the period to 12 months (in which case, optimising the optimisation tool so that the total taxable amount is as low as possible -- for example, instead of two months at €60, one at €45 (not to be taxed) and the other at €75),
• a note stating that a year has only 12 months, thus manual re-arrangement needs to be done.