Create org group management page

Following the shaping of the new version of Account Management in Connect Dashboard, a page must be added to manage org groups and should look like this:

https://www.figma.com/proto/y2uw7SQPzoTmWwlhFldx2B/Nexio-User-Management?node-id=284%3A353297&scaling=min-zoom&page-id=124%3A4116&starting-point-node-id=439%3A347282&show-proto-sidebar=1

Key points:

• The page is displayed on a separate tab called "Groups" (next to "Users")
• Only current org related groups are displayed: those groups are identified by an orgId prefix that is not displayed to the user
• Only the Name, Description and total count of users is displayed on each row
• There is a "create group" button triggering a creation popup with Name and Descritpion fields
• The group edition popup is displayed immediately when creating a group
• There is an icon to edit (description only) and delete on each group row 
• Manage users (i.e Add/Remove users) only in details page: Needs creation of the 2 columns polymer element
• The group details page is displayed when clicking on a group row (i.e list of member users and member groups): only current org related groups are displayed

The new page will only be available by URL for now, we keep the current Account Mngt page available via Menu