This commit replaces the mute/unmute topic button in the message
header bar with a button that allows the user to set the
visibility_policy of the topic to muted, unmuted, followed or inherit.
The button in the message header bar has an icon corresponding to the
current visibility policy of the topic.
In a muted stream:
A click on the button opens a popover with 'Mute', 'Default', 'Unmute',
and 'Follow' options.
In a not muted stream:
A click on the button opens a popover with 'Mute', 'Default', and
'Follow' options. 'Unmute' option is available only when the
visibility_policy is set to 'Unmute'.
The current visibility_policy of the topic is highlighted in the
popover.
Prakhar Pratyush