use external fpm package

[amitu]

Note: This would be trivial after download-base-url in fpm is implemented.

Currently we add something like this to TEMPLATES:

    {
         "BACKEND": "ftd_django.TemplateBackend",
         "DIRS": ["ui"], # <- this is where you would keep your ftd files
         "OPTIONS": {
             "PROCESSORS": ["app.processors.simple_processor"]
         }
     }

Imagine if we could add this instead:

    {
         "BACKEND": "ftd_django.TemplateBackend",
         "OPTIONS": {
             "PACKAGE": "foo.com/package"
             "PROCESSORS": ["app.processors.simple_processor"]
         }
     }

We have deleted DIRS and added PACKAGE to OPTIONS.

In fpm we already have a feature to download dependencies on demand, we can use this feature for main package as well.

Rationale

The advantage would be we can maintain our FPM package independently from our django code.

Both Would Be Supported

We will support both ui folder and PACKAGE option.