Import tasks via CSV (#51)

* Bare start on CSV support

* Move core of CSV importer to operations

* More validations, break out validation function

* Validate dates and TaskList; convert errors to list of dictionaries

* Finish upsert code, and documentation

* Print msgs from the mgmt command, not the operations module

* Handle BOM marks

* Handle both in-memory and local file objects

* Update readme

* Working browser-upload view

* Bail on incorrect headers

* Fix default values and finish example spreadsheet

* Change column order, update docs

* Update index.md for RTD

* First round of responses to PR feedback

* Restore independent summaries/errors/upserts properties

* PR responses

* Split off reusable date validator into separate function

* Fix URLs append

* General test suite for CSV importer

todo/urls.py

@@ -1,10 +1,10 @@
+from django.conf import settings
 from django.urls import path
 
 from todo import views
 from todo.features import HAS_TASK_MERGE
-app_name = 'todo'
 
-from django.conf import settings
+app_name = 'todo'
 
 urlpatterns = [
     path(
@@ -59,7 +59,7 @@ urlpatterns = [
 ]
 
 if HAS_TASK_MERGE:
-    # ensure autocomplete is optional
+    # ensure mail tracker autocomplete is optional
     from todo.views.task_autocomplete import TaskAutocomplete
     urlpatterns.append(
         path(
@@ -83,4 +83,9 @@ urlpatterns.extend([
         'search/',
         views.search,
         name="search"),
+
+    path(
+        'import_csv/',
+        views.import_csv,
+        name="import_csv"),
 ])