[$75] Add API to unarchive an archived group

[jmgasper]

@atelomycterus - A couple minor tweaks to the groups / archive stuff:

1. When returning groups in the API, can we now include the archive flag for that group (true / false)
2. Can we add an endpoint to unarchive a group that had previously been archived (or just tweak the current archive endpoint to allow us to set this true /false)

[jmgasper]

Challenge https://www.topcoder.com/challenges/27cc8d86-a9fa-4982-b9b6-a698d1207097 has been created for this ticket.

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[jmgasper]

@sdgun - This one won't be testable directly - it'll be for admin functionality through the admin app.

[jmgasper]

Challenge https://www.topcoder.com/challenges/27cc8d86-a9fa-4982-b9b6-a698d1207097 has been assigned to obog.

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[atelomycterus]

@jmgasper Please apply PR-topcoder-platform/forums-groups-plugin#66. Thanks!

1. It has been implemented:
   

Converted array keys to CamelCase for standard API output.

2. Implemented. /groups/{id}/unarchive - Unarchive a group
   the achive/unarchive method requires 'Groups.Group.Archive' permission.

[jmgasper]

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