OpenCO2_Sensor Alternative Case

I dropped and smashed my original OpenCO2_Sensor case from this open-source project: https://github.com/davidkreidler/OpenCO2_Sensor. The original case is hard to 3D print with PLA, so I made a simpler one. The old design had built-in buttons (BOOT and RST) on the back, but with PLA they break too easily. My new case needs the back plate removed to use those buttons, which works for me since I only use them once a week or so for updates or calibration.