Bubble Level Mounts for Ender 3

Collection of mounts I hastily put together to mount a bunch of cheap bubble levels (which I got from [this Amazon listing](https://www.amazon.com/gp/product/B09BPYB7T6)) to my Ender 3 to help me make sure that parts of it are mounted level (and stay level).

Having these on your printer is probably overkill! But I was concerned about the x-axis gantry falling out of alignment during long prints on a previous project and I wanted a way to test that.

For mounting the "vslot" mounts, I just used [T-nut M3 drop-in rotating V-Slot](https://www.thingiverse.com/thing:3050607). The "tensioner" mounts can mount with the stock Ender 3 bolts for both the X and Y belt tensioners.