Show applicable mincome limits error on mincome step in group creation

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Problem

When creating a group, the user can enter a mincome that's larger than the app can handle. The error isn't shown on the "3. Minimum Income" step. Instead, the user sees a cryptic error on the unrelated "4. Voting system" step, and only after clicking "Create Group".

Solution

Show a user-friendly error on the "3. Mincome Income" step, where the user can easily understand and correct the error.