Prior to this commit, loaded channels and chats would always be
sorted by date of last message received, with the latest one being
moved to the top of the list.
When new channels or chats are joined, they are added on top of the
list as well, however, when the application is restarted,
those new joined chats would not necessarily show up at the top anymore
becaue nothing keeps track of when a channel was joined, which should
be taken into account when preserving the order.
The changes introduced in this commit solve this by introducing a
new `joined` property on the `Chat` type which gets updated with
the current timestamp whenever a channel is joined.
It also depends on the changes made to the `status-go` client, which
have to land first: https://github.com/status-im/status-go/pull/2158Closes: #1832
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