Add missing activity types

[dahlia]

For now, Fedify is missing some minor activity types.

• [x] Accept
• [x] Add
• [x] Announce
• [x] Arrive: #68
• [x] Block
• [x] Create
• [x] Delete
• [x] Dislike
• [x] Flag
• [x] Follow
• [x] Ignore
• [x] Invite: #80
• [x] Join: #80
• [x] Leave: #80
• [x] Like
• [x] Listen: #80
• [x] Move: #92
• [x] Offer: #76
• [x] Question
• [x] Reject
• [x] Read: #92
• [x] Remove
• [x] TentativeAccept: #92
• [x] TentativeReject: #92
• [x] Travel: #92
• [x] Undo
• [x] Update
• [x] View: #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. https://github.com/dahlia/fedify/pull/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.