v2.60.0 Update

• Slack integration now mentions users with the same email address on the Slack side! → Slack integration must be deleted and reconnected once.
• Project-specific holidays and regular holidays can now be set. On holidays, the Gantt chart will be grayed out and no reminder emails will be sent.
• Members can now be reordered on the Responsible and Ball screens.
• Other design and layout adjustments