This adds throw_alert() and /obj/screen/alert, a system that allows you to do custom hud alerts for any variety of things from "You're too cold!" to mecha status indicators for the pilot.
There's quite a few things that actually got replaced; the
fire/oxy/tox/co2 alerts are all now just alerts, as is nutrition. There's also a number of new alerts, such as blindness, highness, legcuffed, buckled, handcuffed, and probably some more I missed; read code/_onclick/hud/alert.dm and see for yourself!
Additionally, a number of tweaks have been done to resisting code, to make it so that there's an indicator when you're buckled or handcuffed, and can just click the alert to start resisting. This includes a refactor that combines the logic for lockers, holders all into one proc, called container_resist().
Also, the health and internals indicator got moved down one tile each. Needed room for the alerts. If we add the oxygen tank action buttons from /tg/ and remove the internals indicator, the health indicator can go back where it was originally.
Alerts, pictured in the top right.

Because who doesn't want a robotic cat on their head? Adds in the missing code to allow pAIs to actually be picked up, and held sprites for the newer 4 chassis options.
A lot of new defines are now in inventory_sizes.dm, which contains;
All the size identifiers (the thing that tells the game if something is bulky, or w/e).
Storage costs for all the sizes, which are exponents of two, as previously.
A few constants for inventory size.
Also changes all storage item's capacity definitions by basing it off of how many 'normal slots' exist for it. This allows one to change the definition for all of the defines in the file, and everything will follow along without needing to change 500 files. In testing, I made all ITEMSIZE_COST_* defines doubled, and nothing had broke.
The benefit of doing all of this is that it makes adding new weight classes in the future much simpler, and makes knowing how much space a container has easier, as seeing ITEMSIZE_COST_NORMAL * 7 means it can hold seven normal items.
As in, scooped mob holders, like Teshari. If they throw an item, it falls out now rather than being trapped and eventually deleted in their holder object.