Are certain weapons considered two-handed?

Solution 1:

TL;DR
Losing one hand doesn't effect the colonists base ability to aim/shoot the weapon. Losing a hand will only effect their manipulation. Losing two hands still doesn't effect the aiming and shooting time but they can no longer wield a weapon. As long as a colonist has one hand, he/she can use any weapon as usual.

Long
I did some research into the question and ran some tests to see what effects loosing a hand has. The the current effect of loosing one hand is removing 50% of total manipulation. Loosing both hands completely removes all manipulation. When testing this the colonist dropped the weapon and could no longer pick up any weapon.

The colonist with one hand could still use all weapons but only has 50% manipulation. This has no effect on the aim/aiming time of the colonist. I tested this with both colonists and neither of their accuracy or aiming time stats where effected with the loss of hands. This stat can be seen in the information panel.

I've included some screenshots below showing the results of my tests. I did this via debug mode.

Screenshots
Rimworld Tests