MUC autojoin flag should hide them in the chats list

[ivucica]

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Bevor you create a new issue:

- [x] I searched for similar issues and did not find one
- [x] I'm using the latest version available in the [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)

I'm submitting a...:

Feature request (UserVoice request: )

Current behavior:

All chatrooms in bookmarks ~~seem~~ look like they are autojoined by UWPX (until they are clicked). They all initially appear with date when the account first picked up the bookmark, no matter when the last message was posted, making it hard to pick out the ones I care about. The icon is there, but it's still suboptimal.

Expected behavior:

Flag autojoin determines whether a chatroom should be joined. Most of the rooms I have in my bookmarks have it set to false, as I usually don't actually want to autojoin it.

Example of an entry in my PEP storage:bookmarks node:

<conference jid="[email protected]" autojoin="false" name="Biboumi">
<minimize xmlns="xmpp:gajim.org/bookmarks">false</minimize>
<nick>my_nickname</nick>
</conference>

Example of the same entry in my private XML storage jabber:iq:private's <storage xmlns="storage:bookmarks">:

<conference jid="[email protected]" name="Biboumi" autojoin="false">
<minimize xmlns="xmpp:gajim.org/bookmarks">false</minimize>
<nick>my_nickname</nick>
</conference>

I would expect the rooms not to appear on the left side unless I am actually joined in them.

The current appearance out-of-the-box confused me:

Minimal reproduction of the problem with instructions:

Environment:

App Version(s): 
v.0.23.0.0 <!-- Which version of the App are you using (e.g. v.0.2.0) -->

Windows 10 Version Number: <!-- https://en.wikipedia.org/wiki/Windows_10_version_history -->
- [ ] 1809
- [ ] 1803
- [ ] 1709
- [ ] 1703
- [ ] 1607
- [ ] 1511
- [ ] 1507
- [ ] Insider Build (build number: )
- [x] Misc: 1909, I think?

Device form factor:
- [x] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub

Where did you got the APP from?
- [x] [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)
- [ ] Self-build, using a provided release source
- [ ] Self-build, repo cloned at [dd.mm.yyy] <!-- When did you clone the repo! -->
- [ ] Misc, got it from... <!-- Please tell us your source! -->

[COM8]

Yes, this looks broken. I will have a look at it. Thanks for reporting!

[COM8]

When UWPX hides all non autojoin MUCs, where should I keep them then? Do you have any suggestions for that? Since over time they should accumulate at the bottom of the chats list since they do not receive any new messages any more.

An other idea would be to add a filter option for them, which is on by default.