Teamday fixes

[Frajhamster]

There is no Jira ticket, since these are fixes of issues, that have been found on the team day, which means some of the checkboxes below cannot be fulfilled.
Changes:

• Fixed a few German strings
• Added new German string translation
• Removed "Add from local" option from the actors/objects popup menu
• Fixed a crash which happened when trying to paste empty clipboard

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