More specific transcription types

Replace ElementType.Transcription with Paragraph, Line, Word and Character.

arkindex/documents/migrations/0014_auto_20180625_1119.py

+# Generated by Django 2.0 on 2018-06-25 11:19
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('documents', '0013_elementpath'),
+    ]
+
+    operations = [
+        migrations.RunSQL("UPDATE documents_element SET type='word' WHERE type = 'transcription'"),
+    ]