Compare previous billed users count and new one from preview

Problem

If the group has an overage and adds a user that will not increase already existing billable members count we should not show the overage.

Currently we rely on API field hasOverage to show/hide the overage

Proposal

Add one more field willIncreaseOverage that would compare current billed user count and the one from the preview. If the number will be increased return true, otherwise false.