* Add ability to sync all LINE contacts, which is relevant because the
list of recent chats excludes users you haven't spoken to lately.
* Add bot command to list all contacts.
* Allow inviting a puppet to a DM to create a portal for that LINE user,
instead of having to wait for that user to message you first.
Instead of having to view a LINE chat when a media message is sent, send
a placeholder message that gets replaced with the actual media when it's
viewed in Matrix.
