Adds mouse pointers for different ui styles

Sprites are kinda meh but they match the UI styles as close as possible while still remaining visible in darkness and bright things like flashbang overlays.

This is a very basic implementation just to show, hey, we can do this if you want guys. I'm not sure how to make the mouse pointers not look like shit in the rest of the byond windows, but it works fine on the game screen. On the other windows, it updates weirdly and switches back to your OS' pointer at random. I suppose I could add a 'use in-game pointer' preference under the UI style option for people who want to disable it and to circumvent the likely BYOND issues, but anyway, here they are.

![ss 2014-12-27 at 03 06 06](https://cloud.githubusercontent.com/assets/7247232/5561144/c70997d6-8d75-11e4-995b-4e38b190ab59.png)
![ss 2014-12-27 at 03 05 24](https://cloud.githubusercontent.com/assets/7247232/5561145/c8055b98-8d75-11e4-97b2-9d847b7aac7d.png)
![ss 2014-12-27 at 03 05 31](https://cloud.githubusercontent.com/assets/7247232/5561146/c930fd88-8d75-11e4-8e3e-d98c79247561.png)