Make I2C address configurable

[pkb-pmj]

• I2cDevice::release must return address in order for reinit_i2c_device to work
• Should Mpu9250::release return the address? If so, should it be u8 or converted back to I2cAddress?
• Not sure what's the best place to convert I2cAddress to u8
• Obviously a breaking change in the function signatures