create filemanager fields.py file
create an empty form class for filemanager
create empty widget class for filemanager
create an empty class for filemanager field
override constructor for filemanager field with custom parameters

custom parameters for max and min length and path
define attributes for filemanager field and add path handling plus custom form and widget
add small javascript file to open filemanager as popup and allow file selection in admin
add css file for filemanager select field (red dummy square)
add template to render filemanager field (for the widget)
define input type for filemanager widget
add path attribute handling to filemanager widget
override rendering of filemanager widget with custom template and attributes
include filemanager css and js files for widget as media
add missing models import to filemanager fields file
add popup handling to view and templates