Add file caching app

Convert document image cache to use file cache manager app.
Add setting DOCUMENTS_CACHE_MAXIMUM_SIZE defaults to 500 MB.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/file_caching/migrations/0001_initial.py

@@ -0,0 +1,64 @@
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Cache',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=128, unique=True, verbose_name='Name')),
+                ('label', models.CharField(max_length=128, verbose_name='Label')),
+                ('maximum_size', models.PositiveIntegerField(verbose_name='Maximum size')),
+                ('storage_instance_path', models.CharField(max_length=255, unique=True, verbose_name='Storage instance path')),
+            ],
+            options={
+                'verbose_name': 'Cache',
+                'verbose_name_plural': 'Caches',
+            },
+        ),
+        migrations.CreateModel(
+            name='CachePartition',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=128, verbose_name='Name')),
+                ('cache', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='partitions', to='file_caching.Cache', verbose_name='Cache')),
+            ],
+            options={
+                'verbose_name': 'Cache partition',
+                'verbose_name_plural': 'Cache partitions',
+            },
+        ),
+        migrations.CreateModel(
+            name='CachePartitionFile',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('datetime', models.DateTimeField(auto_now_add=True, db_index=True, verbose_name='Date time')),
+                ('filename', models.CharField(max_length=255, verbose_name='Filename')),
+                ('file_size', models.PositiveIntegerField(default=0, verbose_name='File size')),
+                ('partition', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='files', to='file_caching.CachePartition', verbose_name='Cache partition')),
+            ],
+            options={
+                'get_latest_by': 'datetime',
+                'verbose_name': 'Cache partition file',
+                'verbose_name_plural': 'Cache partition files',
+            },
+        ),
+        migrations.AlterUniqueTogether(
+            name='cachepartitionfile',
+            unique_together=set([('partition', 'filename')]),
+        ),
+        migrations.AlterUniqueTogether(
+            name='cachepartition',
+            unique_together=set([('cache', 'name')]),
+        ),
+    ]