Use both the last_moved_timestamp and last_edit_timestamp to show
edited and moved indicators/tooltips in the message list view of
the web app, instead of parsing the message edit history array.
We still maintain and build the message edit history array as it's
used for calculating the narrow terms when there is a near operator
and a message has been moved to a different channel or topic.
Updates the tooltip for message edit indicators to include both
the moved and edited time if a message has been both moved and
edited.
Since we allow calling `add_messages` without checking fetch status,
it can lead to non-contiguous message history due to latest message
being added to a message list without previous messages being
fetched.
To fix it, we only allow adding new messages via message_fetch
which properly sets `anchor` to the last message in the list
before fetching and adding messages to the list.
