Silicon Labs Thunderboard Sense case

This is a case for [Silicon Lab's Thunderboard Sense board](http://www.silabs.com/products/development-tools/wireless/bluetooth/thunderboard-sense-kit)

I've designed this to use the sensors of the board outdoors, but I did not test it yet.
Features:
* Venting hole above the temperature/humidity and the air pressure/temperature sensors. The holes are going upwards to the sensor to avoid water getting in
* 5.3mm hole above the light sensor
* Drain holes at the bottom to remove water possibl