Making vtkACosmoReader take a complete list of files.

vtkACosmoReader needed the user to pick the last file in the series. That was
error prone. Fixing it to allow the user to pick the entire series of files and
vtkACosmoReader automatically picks the last file to extract information about
levels etc.

Change-Id: Ic2e93cf496a9c7fb0acafbab4c340a3443d6c48c
Streaming must resume after interaction.

Makes it possible restart streaming after user interaction. This make it
possible for streaming to resume after camera has moved.

Change-Id: Iaed9d6a4b33c4677edf463557e0693f25fe09254
Enhancements to particle streaming.

Enhancements to particle streaming to allow purging of particles as user zooms
out -- consistent with past versions of the functionality. Also added mcehanism
to show outlines for blocks being fetched as well as change opacity for the
particles.

Updating vtkStreamingParticlesPriorityQueue to make it easier to change the
comparison operation based on the nature of the dataset.

Change-Id: I96d2bee8cc3b4782496a3ecae2f07411a53fa7f0
Merge topic 'fix_particle_streaming' into next

8123ab9 Enhancements to particle streaming.
8817ed1 Streaming must resume after interaction.
abbc0e0 Making vtkACosmoReader take a complete list of files.