Feature/oriented points layer

[seankmartin]

Adds an oriented point layer JSON generator, as well as an encoder for oriented point data as a set of three lines for each point.

The three lines would represent the rotated x, y, and z vectors for each point.

Along with adding this feature, some base annotation encoders and point annotation shader classes that can be used by child classes have been added. This is in an effort to make changes to the overall annotation strategy or shaders easier to propagate through the case base.

[aranega]

All looks good to me :) there is only the question about the "sharding.py" file that we could remove probably if we use the CloudVolume library (which is now a dependency of the project).

[seankmartin]

Hey @aranega , depending on cloud-volume sharding seems to have worked, you can see the changes in b34bb95