This commit adds "close-modal-btn" class to cancel button in
the modal and cross icon.
We do this change because we would add a modal for unsubscribing
from private stream in further commit using confirm_dialog module.
We would need to avoid the unexpected closing of stream settings
on closing the modal which can be done by calling 'e.stopPropagation'
to prevent propagating of events in other elements.
Thus, adding this class will mean that the handler used for stream
privacy modal for this same task will be used for unsubscribe modal
also.
* Currently, the confirm_dialog is used only in
the settings pane, which already has the `new-style`
class in the main `settings_overlay.hbs` file. So,
the confirm modal is rendered correctly there. But to
make it available for use outside of the settings pane,
we add the `new-style` class to the confirm container
itself, without which, the buttons look ugly.
* The other change here is the click handler for
removing the modal element. Previously, when the
modal was closed (with any of the "yes"/"no"/"cross"
buttons), there was a small time interval of around
a second during which the modal had disappeared,
but the background content was still in the faded-out
state. This change fixes this glitch. This glitch was
probably not noticable earlier, because the settings
pane itself causes the background to be slightly faded
out.