Improve automatic emails with temporary urls

This MR targets the improvement for automatic emails concerning validation of new users by supervisors/re-validation of users.

Fixes #542 (closed)

Fixes #550 (closed)

beat/web/accounts/migrations/0012_accounts_tempoary_url.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.26 on 2020-04-27 23:41
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('accounts', '0011_check_all_accounts'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='TemporaryUrl',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('status', models.CharField(choices=[('V', 'Supervisor validates supervisee'), ('Y', 'Self yearly revalidation from sueprvisee')], default='V', max_length=1)),
+                ('url_hash', models.CharField(max_length=32, unique=True, verbose_name='Url')),
+                ('expires', models.DateTimeField(verbose_name='Expires')),
+                ('supervision_track', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='supervisees', to='accounts.SupervisionTrack')),
+            ],
+        ),
+        migrations.AlterField(
+            model_name='profile',
+            name='status',
+            field=models.CharField(choices=[('N', 'New User'), ('W', 'Waiting Validation'), ('A', 'Accepted'), ('R', 'Rejected'), ('Y', 'Yearly revalidation'), ('B', 'Blocked no supervisor')], default='B', max_length=1),
+        ),
+    ]