Importing unused parts of gl-matrix

[donmccurdy]

1672dfe contained a change to how gl-matrix is updated, because its (external) type definitions do not allow the earlier syntax:

// before
import { determinant, getRotation } from 'gl-matrix/mat4';
import { length } from 'gl-matrix/vec3';

// after
import { mat4 as glMat4, vec3 as glVec3 } from 'gl-matrix';

Unfortunately this means we'll be importing more of the library, and probably increasing bundle size. Should try to see if the type definitions can be fixed, or work around this another way.

[donmccurdy]

Fixed in f1caf79. Just reverting the changes for now, TBD fix for type declarations. toji/gl-matrix#423.