Exchange-A-Blade Utility Knife PLA Optimization

This is a remix of the EAB utility blade.

Motivation:
I found that the original EAB when printed in PLA would have the locking mechanism snap off very easily. There was also no way to flush mount the screw and retaining nut.

Overview of changes:
Re-designed the locking mechanism for PLA. (Moved it over and reinforced the piece)
Modified the tolerances around the blade swivel for a 0.4mm hotend.
Reduced size of pocket clip.
Added inset holes for M3 screw and M3 nut.
Chamfered the blade cover.

Two Updates!
1) I added little tabs on the flipping part of the knife so that it is easier to grab.
2) I wasn't happy with the locking mechanism in PLA so I remodeled it to have a metal insert instead. I know, I know. It now no longer works right off the build plate, but after using the original version for months, the plastic just didn't feel safe. Also, the metal/plastic looks really slick.