[Enhancement] Custom media lifecycle scripts (#219)

* Namespaced notification modules under lifecycle

* Added a JSON encoder for all the main model types

* Added startup task to create user script file

* Hook up user script event to media download

* Hooked up media deletion user script

* Added jq to docker deps

* Updated README

lib/pinchflat/utils/filesystem_utils.ex

@@ -5,6 +5,21 @@ defmodule Pinchflat.Utils.FilesystemUtils do
   alias Pinchflat.Media
   alias Pinchflat.Utils.StringUtils
 
+  @doc """
+  Checks if a file exists and has non-whitespace contents.
+
+  Returns boolean()
+  """
+  def exists_and_nonempty?(filepath) do
+    case File.read(filepath) do
+      {:ok, contents} ->
+        String.trim(contents) != ""
+
+      _ ->
+        false
+    end
+  end
+
   @doc """
   Generates a temporary file and returns its path. The file is empty and has the given type.
   Generates all the directories in the path if they don't exist.