Message Editing: View edit history

[jryans]

For an edited message, we should add an edit history dialog (probably accessed by the "edited" annotation) which shows all edits of the message.

• implement basic dialog
• fetch and show history
• date separators
• make pillifying work
• handle emotes correctly
• do pagination (on scroll)
• order messages descending
• style both m.text and org.matrix.custom.html the same
• try not to duplicate styles between event tile and history item too much
• make it work in e2e rooms
• minor style tweaks to align fully with design

[bwindels]

We'll be using /_matrix/client/unstable/rooms/{roomID}/relations/{eventID}/m.replace/m.room.message to paginate through edits.