Currently, the JitsiPopover z-index will cause it to display below
any toast notifications so this changes modifies the z-index
values so JitsiPopover is higher than the notification toasts.

Converting the invite modal includes the following:
- Creating new react components to display InviteDialog. The
  main parent components are ShareLink and PasswordOverview,
  the later handles displaying lock state and password editing.
  These components do not make use of atlaskit as the component
  for input does not yet support readonly, so for consistency
  within the modal content no atlaskit was used.
- Using redux for keeping and accessing lock state instead of
  RoomLocker.
- Publicly exposing the redux action lockStateChanged for direct
  calling on lock events experienced on the web client.
- Removing Invite, InviteDialogView, and RoomLocker and references
  to them.
- Handling errors that occur when setting a password to preserve
  existing web funtionality.

Some atlaskit components, such as field-text, inherit text color.
This is a problem with components that are white as they will
inherit $defaultColor, which is a light gray. So instead, for
the atlaskit modal, set a color for all the form content so it
can be inherited instead.

Atlaskit at times will have localized styling for font-size and
sometimes will not. The button component will inherit its
font-size whereas selectors have localized font-size of 14px. For
consistency, the cancel/submit buttons on the atlaskit modals
will also have 14px. The atlaskit story book examples also use
buttons with 14px font-size.

All z-indexes found in css files have been moved into css
variables. If the z-index is used only once, the variable
name will be the same as the selector it is used in. If
the z-index is used multiple times, then the plain name
of $zindex# was used. This allowed a more confident
moving down of the toolbar so that the new modal dialog,
with z-index 500, could display on top of it.

#1436

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