Add ability to clone all/single events

[marcus-sonestedt]

Is your feature request related to a problem? Please describe.
Usually events are pretty similar from one year to the next, and within one year (races/track days/bbqs) so copying them with predefined tasks would help.

Describe the solution you'd like

• A clone button which clones all data except assigned members to tasks and the date

Describe alternatives you've considered

• Excel export and selective import might work, if there was a button in the web UI to do that.