Always use random filenames for images

Gwicke had a concern when he did a security look through that filenames
could be used to cause damage to the latex engine / the box. Previously
we escaped some stuff and then fell back to using the tmp module -
this just uses the tmp module directly avoiding all escaping and collision
problems.

Change-Id: I3520ae6ab7f1d68b6d285c023ef08e547193a34f
Update to readable-streams v1.1.x

Change-Id: Ibad3d82484b78a882216a930915e8dc4fc4ec1c5
Use 1.0.x branch of readable-stream

Change-Id: Id50c289d01805094b51096ef2a83974602598945
Per: I179c8e885bc25f29bb169d4acdc8e06a4639378d