Additional filter canister designs

[stephen304]

The current canister designs we have are all pretty long. For cheek-mounted canisters, it would probably be nice to have a design more like a pancake. Additionally, someone needs to determine what minimum internal volume we need for these designs to work for our desired usecases, in order to avoid making the canisters unnecessarily large.

We should also catalog these external designs somewhere (note: these are untested):

• https://www.thingiverse.com/thing:4236518
• https://www.thingiverse.com/thing:3858646

This honeywell north organic vapor cartridge seems to be only 4cm in length.