Minor fixes

Set all SS logs to use storage_service.log (instead of mixing with
storage-service.log). Fix 404 exception.
Space: Move path mangling to Space

move_to_storage_service expects the source path to be absolute, and the
destination path to be absolute inside the staging path. Since this is
common, move it to Space.
Models: Split models.py into several files

refs #7135

No other changes made, for ease of rebase.
Models: fixes for split locations

Add app_label to all models to work with split locations. Fix pep8 related
changes, made protocol spaces and location purposes alphabetical.
Clean up constants.py

Import models and forms, instead of individual classes. Move everything
inside PROTOCOL definition.
Duracloud: Stub out Space

refs #7133

Add empty Space, form, constants etc.
Duracloud: Add fields

refs #7133

Add fields to Duracloud Space. Update places to match: constant, forms,
migration, fixtures, test.
Duracloud: Add helpers

refs #7133

Add session with auth for use with all the other functions and
constructor for duraspace URL.
Duracloud: Add move from SS

refs #7133
Duracloud: Add move to SS

refs #7133