calendar: remove 'month' and 'shortmonth' from configuration

[andreaschu]

As a Zofar-user I want a reduced configuration to it's neccessary (configurable) elements. Since months and shortmonths are stable, I don't want to define it for every calendar.

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As a Zofar developer I want to have it saved in the composite component.

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DoD:
calendar works after shift as it does before:

• months are displayed correctly
• display reacts on language switch