Replace POST Model Files API with New multipart-upload API

[pjcross]

Integrate new API into existing wizards. From Tim's email of 9/21/2015:

New API documentation:

• http://slycat.readthedocs.org/en/latest/POST-Uploads.html
• http://slycat.readthedocs.org/en/latest/PUT-Upload-File-Part.html
• http://slycat.readthedocs.org/en/latest/POST-Upload-Finished.html
• http://slycat.readthedocs.org/en/latest/DELETE-Upload.html

Old API made obsolete by these changes:

• POST Model Files - still implemented in the server and client libraries, but removed from the documentation.

Example code:

• slycat/web-server/plugins/slycat-multipart-upload-demo

Running the example code:

• Configure your web server to load the slycat-multipart-upload-demo plugin.
• Point a browser to https://your-slycat-server/pages/multipart-upload-demo
• Use the file chooser button to point your browser to a copy of slycat/data/cars.csv (demo is hard-coded to work with this file).
• Click “Upload”.
• The plugin code splits the file into two pieces, uploads them separately to a CCA model, and finishes.
• Visit the new model to see that everything looks the way it should be.

[Mletter1]

note that these lines need to be added to the config.ini file

upload-session-timeout: datetime.timedelta(minutes=15)
upload-store: "/var/lib/slycat/upload-store"