Replace all X.imread calls with read_image

read_image (from timestream.parse) is a wrapper around scikit image's
imread using freeimage. This change allows us to use a single image
reading function to avoid weird bugs where we have several image reading
functions at once. This also allows us to change our mind as to which
image IO library to use and only need to change one function.

Changes to be committed:
      modified:   timestream/__init__.py
      modified:   timestream/manipulate/pipecomponents.py
      modified:   timestream/parse/__init__.py