Adding multiple contacts to a group

[abhi1203]

Is your feature request related to a problem? Please describe.
Right now staff users will have to add a contact to a group one by one. We needed a faster mechanism for this.

Describe the solution you'd like
Solutions are as per the design:

1. A button to add contacts to group: https://www.sketch.com/s/ba323b85-11d7-4687-8a19-681a32132bab/a/evpd0p
2. Popup to select the contacts to be added to group: https://www.sketch.com/s/ba323b85-11d7-4687-8a19-681a32132bab/a/J0r3O9
3. Confirmation for addition. https://www.sketch.com/s/ba323b85-11d7-4687-8a19-681a32132bab/a/vYyGD3

Additional context
We had designed for this earlier but i think it didn't get discussed properly. Hope we can add it now.