sub: Rename "count" to "credits"

[vivainio]

We should use "credits" throughout the service instead of "count" (with T&B, one "try" consumes 1 credit, or 1 credit could be 1 second for time limited game)

[juhanak]

URL parameter change: count changed credits
JSON response change: {"uses_left": x, "expires": x} -> {"credits_remaining":x, "time_remainig":x}