Add Raspberry Pi Sense HAT-related drivers

[MacroYau]

This PR includes the following drivers related to the Sense HAT:

• 5-button miniature joystick
• ST LPS25H barometric pressure and temperature sensor
• ST HTS221 relative humidity and temperature sensor

The Sense HAT metadriver has been updated accordingly. Only the Sense HAT IMU driver is missing now.

This is a revision of #22, and it has been rebased to the master to date.

[MacroYau]

@proppy I attempted to refactor the Sense HAT driver to accommodate the shared I2cDevice instance. This will break the compatibility with the v0.1 LED matrix driver. Any comment?

[knobtviker]

Any plans to have this merged?

[rachitmishra]

Umm, when are we merging this? Is any help required?

[proppy]

@rachitmishra sorry, I still have to review and make the modification suggested in https://github.com/androidthings/contrib-drivers/pull/24#discussion_r98287110

[umairvatao]

Please merge it soon