Make GPIOPortMCP23017 more general and support native GPIOs

[marianopeck]

Right now, GPIOPortMCP23017 works with a device. The API of that device is basically a subset of I2CDeviceGPIOMCP23017. I believe that subset of functionality / API should eventually be moved up in the hierarchy (to I2cDevice or GpioBusDevice). That way, GPIOPortMCP23017 could be renamed to GPIOPort and depending on which device you pass, it would use either the GPIOs of MCP23017 or the native ones.

At this point, it would also be interesting to think if those GpioBusDevice and similar GPIO* classes should be renamed to Pigpio*.