Prepare for React 16.

* ref(invite): use AtlasKit for invite modal buttons and inputs

- Convert button to AK Button.
- Convert inputs to AK FieldText.

* remove noop, replace with custom empty func

With the upgarde of @atlaskit/icon to 7.0.0, the size prop
essentially became required to maintain its appearance in the
jitsi app, otherwise it'll unexpectedly try to take up the
available space and cause minor display issues.

DialInNumbersForm has been modified to display a conference id to be used for
dialing into the conference. The changes include:
- Requesting the conference id and adding the conference id to the redux store
- Displaying the conference id in DialInNumbersForm
- Modifying the copy behavior to support copying the new message to clipboard
- DialInNumbersForm does not display until all ajax requests have completed
  successfully. This eliminates the need for the REQUESTING state.

Create a new React Component for displaying a list of dial-in
numbers. The Component will fetch the numbers from a new
numberRetreviewUrl key/value set in config. If not present in
config, the Component will not be displayed.