Review and revise python dask interface

Created by: dyang37

Review and revise python Dask interface:

• Review and get group agreement on the python Dask interface.
  1. Design and implement configuration files. a). Single node. b). Multiple nodes: Lilly Cluster and Purdue Cluster. c). Document each item in the configuration file.
  2. Design and implement get_cluster() function. a). get_cluster() read configuration file and return a cluster object.
  3. Design and implement a Dask parallel function to do 3D reconstruction on muliple time points. a). Use a cluster object to distribute the recon3D function and input data(sinogram, angles) to multiple nodes.