Fix: #151 saving edited events via modal

[LexMonster]

The edit modal was pushing the "edited" event into the calendar events instead of replacing it.

Pull Request Description

When the addEventWithModal is called with an event as parameter it now assumes that it is editing. As such it will replace the old event with the new event based on its id instead of just pushing it to the data to be saved.

Related Issues

Fixes #151

Checklist

• I have read the contribution guidelines and code of conduct.
• I have tested the changes locally and they are working as expected.
• I have added appropriate comments and documentation for the code changes.
• My code follows the coding style and standards of this project.
• I have rebased my branch on the latest main (or master) branch.
• All tests (if applicable) have passed successfully.
• I have run linters and fixed any issues.
• I have checked for any potential security issues or vulnerabilities.

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fix: Saving edited events via modal no longer duplicates events (close #151). Thanks @LexMonster.
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