Power Strip support extended by additional attributes

[syssi]

(Closes: #286)

[houndci-bot]

blank line at end of file

[coveralls]

Coverage increased (+0.09%) to 71.169% when pulling c5f0369 on syssi:feature/powerstrip-extended into 056954c on rytilahti:master.

[coveralls]

Coverage increased (+0.09%) to 71.169% when pulling d6dceba on syssi:feature/powerstrip-extended into 056954c on rytilahti:master.

[rytilahti]

Looks ok to me, unfortunately my strip (zimi v2) doesn't support any of these new ones, here's the complete output:
{'power_price': 999, 'power_factor': 0.0, 'power_consume_rate': 4.19, 'temperature': 53.89, 'elec_leakage': None, 'voltage': None, 'mode': None, 'power': 'on', 'current': 0.05, 'wifi_led': 'off'}