[Feature] Edit an activity

[sthewissen]

What

• [x] Users should be able to edit an activity.
• [x] Editing opens the wizard at the technology step.
• [x] Existing data is pre-filled
• [x] SelectedItem changes should not have to be triggered to continue.
• [x] Required fields are validated.

[sthewissen]

Missing right now: validation and the QoL upgrades already mentioned in #4