API for custom default values during parsing.

[sovdeeth]

Description

Adds an api for declaring custom default values during parsing. Does not apply to runtime defaults like arithmetic.
The goal of this is to provide a slightly easier method for section to provide section-specific defaults without having to create an entire custom event and change the context.

I think this implementation might be a little rough and would welcome critiques.

Example:

		// Add custom default value
		data.addDefaultValue(Number.class, new SimpleLiteral((Number) 7, true));

		// parse section with custom value
		loadCode(sectionNode);

		// remove custom value
		data.removeDefaultValue(Number.class);

---

Target Minecraft Versions: any
Requirements: none
Related Issues: none

[sovdeeth]

Just realized this needs to support multiple layers of default values. Will fix Friday.

default value A:
  default B:
    # default is B
  # default should be A

[sovdeeth]

I would like some thoughts on how/whether to handle cases where context completely changes.
Perhaps a clearDefaults() and restoreDefaults() method? Maybe defaults should be tied to event/a context generic?
not sure, would like suggestions

[APickledWalrus]

This looks pretty good. Just have a few comments I'd like discussion on before merging