Hepa Filter mount - remix

Probably not needed, but for my own peace of mind i beefed up the filter mount, which is part of https://www.thingiverse.com/thing:2394452

changes;
- bottom plate is thicker
- the legs are wider and thicker
- the mount hole type changed from countersink to borehole to facilitate head cap screws

The mount hole footprint and inner circle of the legs remained the same.