cbv edit: form_kwargs: don't set formdata, let flask_wtf do it

we were omitting request.files. flask_wtf based forms handle this automatically
cbv: base_template, chain_create_allowed in __init__

it allows customization without subclassing, passing parameters in as_view()
cbv create: add breadcrumb item with create button title
frontend stuff: use views.objects CBV for view/edit/create/delete; add missing templates
widgets: linkify_url: use fa-external-link icon