Various Refactorings

[mccreery]

This branch just got way out of hand so I'm merging it all in so I can finish each part up in separate branches.

• HudElement type paramaterised for rendering context
• Elements moved to registries instead of a static list
• Removed useless addSettings method in favour of constructor
• New OverlayContext object (planned: include layout manager in this param object)
• Replaced static sorter with registry sorters
• Overlay hook outside of HudElement
• Planned: separate hook for mob info (note: right now there is no mob info visible)
• Removed default position for elements (clutter on "god class")
• Restore a standard GL state before each element is rendered
• Fix corrupt GL flags using a GlStateManagerManager
• Directly use forge events instead of OverrideElement

Not everything is guaranteed to work here (see bold above) but I need master to be up to date and this branch is just not very continuous integration-y.

[mccreery]

Planned: right now the text elements all have the same direction options so some of the custom position code goes unused. This will have to be fixed later for feature parity.