More onboarding improvements (#83)

* Improved custom YYYY-MM-DD output template option

* Clarified embedding vs. downloading on media profile form

* Improved form helpers more; Added a helper to every field

lib/pinchflat_web/controllers/sources/source_html.ex

@@ -14,7 +14,7 @@ defmodule PinchflatWeb.Sources.SourceHTML do
 
   def friendly_index_frequencies do
     [
-      {"On Create", -1},
+      {"Only once when first created", -1},
       {"1 Hour", 60},
       {"3 Hours", 3 * 60},
       {"6 Hours", 6 * 60},