Initial support of working with package definitions

Support the following operations:
* create (upload)
* download
* delete
* categories (get list of available category names)

Also support get, get_logo and get_ui operations for AppCatalog.

Use the `requests` library to encode form data parsed by Django back
into multipart/form-data (as murano-api expects uploaded package data
to be in this format).

Change-Id: Id83f9960e0ee9a67be8ecd37a9a4ff18cd1f21fa
Partially-implements: blueprint service-defitions-migrate-to-apps-ui