Atmos Overhaul - Phase 2

Continuing on from [phase 1](#5362), I present... phase 2 of the atmos overhaul!

**TL;DR - This makes pipes pretty.**

### Features
- Atmospheric devices now have a shared icon cache that they assign overlays and underlays from. The icon cache generates one of each possible pipe at round start (only about 500KB of image objects), then assigns them as requested when a pipe updates (connected, disconnected, painted, etc.). The cache is checked before being referenced and regenerates if something were to go horribly wrong (this might cause a lag spike on live servers, but is highly unlikely to occur, and regenerated instantly on my local server).
- Pipes now have their own color definitions. Pipes can only have a color variant if they are added to the global "pipe_colors" list. The cache auto generates color variants at round start based on the pipe color list, so adding pipe colors is now as simple as adding a color to the list (theoretically this could even be done mid game).
- Device ends (the bit that connects pumps, valves, vents, etc. to other pipes) now match the color of the connected pipe, resulting in seamless color transitions between devices and pipes. Manifolds have their own behavior, matching their color to the connected standard pipe, unless another manifold is connected, in which case they only match if they are the same color manifold.
![I don't know why you would do this, but you can!](https://cloud.githubusercontent.com/assets/6357112/3568212/a5b248b0-0b2c-11e4-97fe-430b9398cc5b.png)

### Updates
- Updated omni devices to use the shared cache.
- Updated "hidden" air scrubber icon to be a circular inset if it is embedded in a floor (yell at me if you think this is ugly and I'll change it back.
- Cleaned up a lot of pipe code, converting it to absolute paths and removing old commented out code.
- Updated pipe painter to use the pipe color list.
- T-ray scanners now make transparent pipes visible by adjusting the pipes alpha channel.

> ![tray](https://cloud.githubusercontent.com/assets/6357112/3568256/fb34e2de-0b2c-11e4-82bb-f80b22fe43fe.PNG)

- Expanded tank capacity and resprited them (I'm intending on doing a complete rewrite/resprite in phase 3, but this will do for now).

> ![tanks](https://cloud.githubusercontent.com/assets/6357112/3568276/3c071386-0b2d-11e4-80e9-f248e9500426.PNG)

- Enhanced pipe checking debug command.
```
Checking for disconnected pipes...
Unconnected pipe located at 172,114,4 (the Construction Site Atmospherics)
...
Unconnected pipe located at 174,121,4 (the Construction Site Atmospherics)
Checking for overlapping pipes...
Overlapping pipe (Air supply pipe) located at 113,78,1 (the Engineering Hallway)
Overlapping pipe (Scrubbers pipe) located at 150,81,1 (the Virology)
Overlapping pipe (Air supply pipe) located at 143,85,1 (the Operating Theatre 2)
Overlapping pipe (Air supply pipe) located at 151,88,1 (the Virology Access)
Overlapping pipe (pipe) located at 102,91,1 (the Aft Primary Hallway)
Overlapping pipe (Air supply pipe) located at 151,98,1 (the Patient Wing)
Overlapping pipe (Scrubbers pipe) located at 125,169,1 (the Detective's Office)
Overlapping pipe (pipe) located at 57,148,4 (the Listening Post)
Overlapping pipe (pipe) located at 174,189,5 (Isolation Cell)
Done
```
(Yes that's on our current map)

### Fixes
- Fixes #4823
- and numerous other visual irregularities with pipes

### Issues
- The map in Dream Maker is a bit broken due to people setting the icon variables instead of using the pipe variants. This is fine at runtime due to the pipe code being clever, although it may result in a few grey pipes where people have set the color var to something not in the pipe color list. I'll go through and tidy all this up in another PR after this is merged.
- It's going to be a pain to code review since I removed all the relative paths in most of the files I touched.

At this point I can pretty much clear out all the old pipe dmi's if that wont cause issues with downstream repo's? (unless someone wants to hold onto them for nostalgia's sake)

@Donkie feel free to steal some ideas for /tg/, this is inspired by [your PR](https://github.com/tgstation/-tg-station/pull/3611) afterall

And one final image of how Atmosia looks after the update:
![Atmosia](https://cloud.githubusercontent.com/assets/6357112/3568426/668106d2-0b30-11e4-8e9a-98b358122ed6.PNG)