Moving core cutout logic, adding views, and using the REST API

[thejohnhoffer]

These changes allow the viewer to use the request method as defined in restapi.py. This pull request additionally enacts the following server-side effects:

restapi handles views and formats

• Incorporates the notion of 'views' of the data
  • views by default include 'grayscale', 'rbg', and 'colormap'
• Allows a request for a 'zip' file format in addition to 'png', etc
• Reuse of functions to make each call simpler

move cutout logic to datasource

• Implements a standard 'load_cutout' method
  • the 'load_cutout' method calls the 'load' method
  • the 'load' method acts on single images or tiles of self.blocksize
  • the 'load' method may be overwritten for each specific datasource.
• Implements a standard 'seg_to_color' method
• Renames the 'get_dataset' method to 'get_channel'
  • better reflects the assertion that each datasource holds one channel

normalize all datasources

• Removes 'seg_to_color' methods inherited from the parent datasource
• Removes the now deprecated 'segmentation' flag from the load call
• Assures the parent DataSource.index method is called for each
• Removes load_tilespec_cutout and broken commented methods

remove cutout logic from core

• Adds 'load_view' method to the core to better manage color and id specific requests
• Removes now deprecated 'segmentation' and 'synapse' flags
• Removes core cutout logic
  • The cutout logic has been moved to the DataSource.load_cutout method
  • Segmentation and Images are loaded in the same way now

These bugs must be addressed before merging:

• Loading uint32 id channels to an image with the 'grayscale' view causes problems