Lot of fixes and small improvements

[HugoGresse]

• add speakers csv export, close Feat: speaker csv export #217
• fix sponsors event counts, close Bug: Sponsor count at the top is not right #207
• add image size and type in the side panel, close Feat: Display image sizes in the side panel #215
• ask for event dates on event creation + aufoFocus, close Feat: ask for event dates when creating a new event #216
• fix copy schedule button, close Bug: copy table in schedule not working #208

[github-actions]

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