JZ: Rename common.pip to base.pip
JZ: Cap dj under < v1.7 (to get latest 1.6.X)
JZ: Add requirements readme
JZ: Add requirements readme
JZ: Update `.travis.yml` for requirements changes.

requirements changes => #640
Merge remote-tracking branch 'origin/reorganized_requirements'

* origin/reorganized_requirements:
  JZ: Update `.travis.yml` for requirements changes.
  JZ: Add requirements readme
  JZ: Add requirements readme
  JZ: Cap dj under < v1.7 (to get latest 1.6.X)
  JZ: Rename common.pip to base.pip