Added template for uploading files.
Added an upload directory for each model.

Added
=====

* On model creation, a directory (whose name is the same as its id)
  is created in the uploads directory.
* On model deletion, everything under this directory is removed.
Changed to use new uploadform template.
Added models/upload command to upload a file to a model upload dir.
Merge branch 'master' of https://github.com/csdms/wmt