Add missing activity types

[dahlia]

For now, Fedify is missing some minor activity types.

• Accept
• Add
• Announce
• Arrive: #65: add Arrive to vocab #68
• Block
• Create
• Delete
• Dislike
• Flag
• Follow
• Ignore
• Invite: Add more missing vocab items #80
• Join: Add more missing vocab items #80
• Leave: Add more missing vocab items #80
• Like
• Listen: Add more missing vocab items #80
• Move: Implement missing activity types #92
• Offer: Add Offer class to Activity Vocabulary API #76
• Question
• Reject
• Read: Implement missing activity types #92
• Remove
• TentativeAccept: Implement missing activity types #92
• TentativeReject: Implement missing activity types #92
• Travel: Implement missing activity types #92
• Undo
• Update
• View: Implement missing activity types #92

In order to add a new activity type, add a YAML file in the vocab/ directory. If the name of an activity type is FooBar it would be vocab/foobar.yaml.

[randy5235]

@dahlia Here is a single missing activity for Arrive. #68

Assuming this looks correct and I haven't missed anything. I can submit more of these missing activities. Didn't want to give you a giant PR to look through for my first contribution.