Miningpool settings

We opened several special ports for the miners with different difficulties:

Difficulty: 4096 - 8192 (> 10 Mh/s)

- minigpool.gravio.net:3333

Difficulty: 2048 (1-10 Mh/s)

- minigpool.gravio.net:3334

Difficulty: 32-128 (< 1 Mh/s)

- minigpool.gravio.net:3335