Schema updates

[pjcozzi]

This is a pull request from the schema branch to a new spec branch where I will make spec changes (maybe in time for GDC, no promises though!). Once the schema and spec are synced, I'll open another pull request to merge spec to master.

This brings the JSON schema up-to-date with the glTF JSON produced by the converter in master. This still needs a few things before merging.

• Format should support references and inline data #68 (converted update needed)
• Animation: input parameter type #158 (converted update needed)
• JOINT_MATRIX or JOINTMATRIX? #187 (converted update needed)
• Remove confusion between node id and jointId #216 (converted update needed)
• Accessor type values #232 (converted update needed)
• Should image have a name property? #235 (converter update needed, perhaps not right away)
• Use accessor for inverse-bind matrices #238 (converted update needed)
• Technique parameter questions #239 (converted update needed)
• More consistent description properties throughout
• Update the states schema for state parameters should be an array instead of a list of named parameters #85 (could be done later)

There are several issues open with the specification label, but we don't need to address all of them right away. I am more concerned about getting the schema in sync with the converter and then keeping them in sync.

We will also have a small open-source JavaScript library that takes a root glTF object and adds missing properties that have default values, e.g., use identity if matrix.node and TRS properties are undefined. This will make it easy to work with the converter option that excludes properties set to their default values. The source is currently here, but it needs more testing and to be moved to its own repo.

[denisjarus]

Captain obvious here, noting that a single tab used for indentation in some of these changes, while the original code uses four spaces.

[fabrobinet]

@pjcozzi do you think you can you merge this PR this week ?

[pjcozzi]

No, it will be the week of August 4 given the August 1 Cesium release.

[pjcozzi]

@fabrobinet I am closing this and will re-open a PR from schema-8 shortly - I just need to tweak the render states and read over the README.md.

[fabrobinet]

ok @pjcozzi thanks for the heads up and the hard work on that one