Remove unused I2CDriver properties and memory fixes

[brentru]

• Removes unused DriverType_t enum
• Makes sensorAddress a getter/setter within I2CDriver base class: setI2CAddress and getI2CAddress
• Properly allocates and deallocates memory for each sensor driver.
  • Destructors do not unnecessarily reset variables or set pointers within drivers to NULL.
• Sensor drivers pointers are properly deleted and removed from the vector, instead of simply being erased.

[ladyada]

im a little paranoid about having public variables because people could set them by accident, unless you mean that?

[brentru]

@ladyada I wanted to simplify the src/drivers/WipperSnapper_I2C_Driver.h interface, but I can also refactor it to utilize getters/setters to wrap these variables (sensorAddress, isInitialized) as private members.

[ladyada]

i think its best to do so, in case something else comes up! its too easy for folks to accidentally set em especially as we get contributors!

[brentru]

@ladyada I've made a good # of modifications since the original PR comments and am requesting a re-review.