[cli] adding reference type and auto-repeater generate syntax

[nilslice]

This PR contains some updates to the CLI a bit to add the ability to generate references to other content types.. here's the syntax:

$ ponzu gen c author name:string bio:string:textarea city:string year_joined:int
$ ponzu gen c article title:string author:@author,name,city content:string:richtext photos:"[]string":file

The trailing ,name,city suffix to author:@author set the displayed option names in the select dropdown inside the CMS. If you leave them blank, it defaults to Author: {{ .id }}

Additionally, any []T slice type i.e. photos:"[]string":file in the example above, will automatically generate a editor.FileRepeater, or the "Repeater" for the view specifier (as long as one exists).

Currently, there are "Repeaters" for file, select, and input which will each have their Repeater generated automatically when accompanied by a []T type

For example:
$ ponzu gen c gallery images:"[]string":file => editor.FileRepeater()
$ ponzu gen c gallery images:"string":file => editor.File()

Side Note: you never specify the view type (file, select, richtext etc) for a reference, i.e. @author.. it will always be a reference.Select or reference.SelectRepeater if you pass []@author