Create new loader for raw data

[frasercl]

Use Case

• As a developer, I'd like to easily create Volumes as mocks to unit test both Volume and the loader API.
• As a developer, I'd like to use the same API to load raw data arrays (in nbvv, e.g.) as remote, formatted data.

Solution

Add a new raw data loader which implements IVolumeLoader. We should not have to modify LoadSpec to accomplish this. The loader should receive a TypedArray (or an array of TypedArrays representing one channel, or an array of arrays representing time points and channels) when createVolume is called, and hold on to it for when loadVolumeData is called.

Write good unit tests by using this new loader to create mocks.

Future work: update website-3d-cell-viewer, nbvv to load raw data via this path.

[toloudis]

Turns out this has become important to get nbvv up and running again.