This PR adds a function to disable the subscribers tab for private
streams if a user is not subscribed to the stream and is not an admin.
We also live update the state of subscribers tab on changing privacy
of stream.

Completing #21537 opened by @Zoronium. Made a few improvements to
directly use can_view_subscribers function, enabling "General" tab in case
subscribers tab was opened when

One of the biggest things that will make it harder for new users coming for reddit is to find Lemmy's website itself.
I recently moved to Lemmy from reddit and took me 10 mins just to find lemmy, whenever I searched up Lemmy, this is what popped up instead.
![Screen Shot 2021-02-26 at 10 16 33 AM](https://user-images.githubusercontent.com/71905307/109318440-cc2ec780-781b-11eb-9ad7-286baccb0d78.

Probably a low priority issue, but currently users can just adjust the maxlength attribute of the username field to get usernames longer than the 60 by default, and can cause text in the overlays to overflow. Not really critical, but maybe a small consideration to make.

(For the UI, something like text-overflow: ellipsis would suffice for usernames to prevent major breakage)

Version

2.34.0

Flavor

GUI (Graphical User Interface), CLI (Command Line Interface)

Export format

No response

Details

##Both CLI and GUI are giving out the same error while trying to export the chats,

.NET Runtime 6.0 is installed before running as prompted

• GUI
  ![image](https://user-images.githubusercontent.com/59572141/164885904-3053278d-2447-4f43-b88a-1a0f36b1bf3

Describe the bug
When a form, sent via an adhoc command, contains a field named "username", it is not displayed at all.

Expected behavior
username is a valid field name, so the form should be displayed

Environment:

• Desktop
• Firefox
• Converse.js version [e.g. 4.2.0]

Additional context
I commented a minimal example here: https://github.com/conversejs/converse.js

I cannot reproduce this with the default usage of botui : the issue appears only when botui is part of a larger VueJS app.

When a markdown image is inserted in a message, it is immediately hidden if another message is displayed after.

botui.message.add({
	content: 'Hello World'
});
botui.message.add({
	content: 'Here is a picture : ![](https://www.google.fr/images/branding/g