Refactor: update `ImageInfo`

[frasercl]

Problem

Resolves #131: Volume receives a type called ImageInfo on construction which contains essential information about the volume's dimensions. This type is based on the JSON schema used by JsonImageInfoLoader, which is not particularly suited to being a general volume information format:

• It is specific to the way JsonImageInfoLoader expects data to be represented (as a series of pre-atlased images, each containing up to 4 volume channels in their r/g/b/a components).
• The JSON is generated from a Python script and uses snake_case. We have to ask eslint to ignore snake_case whenever it's used.
• Because it is read in from JSON directly, it cannot take advantage of Three.js's native vector types.

Solution

• Create a new, more general ImageInfo type, using vectors and camelCase and names that make sense.
• Move the current ImageInfo into JsonImageInfoLoader, rename it JsonImageInfo, revert it to exactly represent the stored JSON, and have the loader convert between the old and new type.
• With more data being represented as vectors, I spotted some shader code that could be more vectorized, so I did that.

[ShrimpCryptid]

Hey, I'm seeing some artifacting/weird slicing behavior? Is this a setting I have misconfigured or is this happening for you too?

[frasercl]

Hey, I'm seeing some artifacting/weird slicing behavior? Is this a setting I have misconfigured or is this happening for you too?

Could you check that you have the latest version of this branch? I also saw this behavior and fixed it (or attempted to) in 4c143f9.

[ShrimpCryptid]

Hey, I'm seeing some artifacting/weird slicing behavior? Is this a setting I have misconfigured or is this happening for you too?

Could you check that you have the latest version of this branch? I also saw this behavior and fixed it (or attempted to) in 4c143f9.

Okay, yes, that fixed it.