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/templates/todo/import_csv.html

@@ -0,0 +1,85 @@
+{% extends "todo/base.html" %}
+{% load static %}
+
+{% block title %}Import CSV{% endblock %}
+
+{% block content %}
+  <h2>
+    Import CSV
+  </h2>
+
+  <p>
+    Batch-import tasks by uploading a specifically-formatted CSV.
+    See documentation for formatting rules.
+    Successs and failures will be reported here.
+  </p>
+
+  {% if results %}
+    <div class="card mb-4">
+      <div class="card-header">
+        Results of CSV upload
+      </div>
+      <div class="card-body">
+
+        {% if results.summaries %}
+          <p>
+            <b>Summary:</b>
+          </p>
+          <ul>
+            {% for line in results.summaries %}
+              <li>{{ line }}</li>
+            {% endfor %}
+          </ul>
+        {% endif %}
+
+        {% if results.upserts %}
+          <p>
+            <b>Upserts (tasks created or updated):</b>
+          </p>
+          <ul>
+            {% for line in results.upserts %}
+              <li>{{ line }}</li>
+            {% endfor %}
+          </ul>
+        {% endif %}
+
+        {% if results.errors %}
+          <p>
+            <b>Errors (tasks NOT created or updated):</b>
+          </p>
+          <ul>
+            {% for error_row in results.errors %}
+              {% for k, error_list in error_row.items  %}
+                <li>CSV row {{ k }}</li>
+                <ul>
+                  {% for err in error_list %}
+                    <li>{{ err }}</li>
+                  {% endfor %}
+                </ul>
+              {% endfor %}
+            {% endfor %}
+          </ul>
+        {% endif %}
+
+
+      </div>
+    </div>
+  {% endif %}
+
+
+  <div class="card">
+    <div class="card-header">
+      Upload Tasks
+    </div>
+    <div class="card-body">
+      <form method="post" enctype="multipart/form-data">
+        {% csrf_token %}
+        <div>
+          <input type="file" name="csvfile" accept="text/csv">
+        </div>
+        <button type="submit" class="btn btn-primary mt-4">Upload</button>
+      </form>
+    </div>
+  </div>
+
+{% endblock %}