Hydroponic plant holder

Update: Check out the [Mk2 design here](https://www.thingiverse.com/thing:3490493)

This is a hydroponic plant holder for a mistponics / fogponics project I'm working on.

It's designed to print without supports, allow decent fog flow to the roots and it curves out at the top to create a seal.

See the stage 1 write-up here: [Mistponics - Ultrasonic hydroponics system](https://www.pointandy.com/pointandymake/2017/11/2/ultrasonic-hydroponics)