Add Square Terminal support to Cin7 POS

Square is a top payment processor, clean terminals, smooth UI, low rates. The little Square Readers already interop with Cin7 POS iOS platform app, and require added tablet hardware with bluetooth interface to function. The WiFi+Ethernet T2 terminals, however, do not interop with Cin7 POS browser implementation. So each transaction amount must be hand-keyed and there is no signal from the terminals into Cin7 to confirm successful transaction ID, $ amount, etc. We would love to see the terminals enabled via Cin7 POS browser implementation.