This is a prep commit to add the status emoji feature.
We update the templates associated with the emoji
picker to add class `status_emoji` to `emoji` in the
popover. So we can later add the events when the user
selects the emoji.
We also update the functions in `emoji_picker.js` to
support opening emoji picker popover in the 'set_status_
overlay`.
We also increase the `z-index` of the `popover-flex`
class (This class is only added to popover-emoji content
if the view is mobile), so in the mobile view the emoji
popover doesn't go behind the '#set_user_status_modal'.