[CHARGER] OCPP integration support

[kljakobsen]

Add support for the OCPP integration, so all EV Chargers there is local integrated to HA via OCPP is supported.

https://github.com/lbbrhzn/ocpp/

I assume this it quite easy, since it is all in HA altrady.

the important entities exposed by the OCPP integration is:
number.charger_maximum_current - Max allowed current on all phases (1-3) to the EV
switch.charger_charge_control - switch control to on/off charging

[dirkgroenen]

@kljakobsen please have a look here and let me know if this works for you: #47

[kljakobsen]

see comment in PR #47