Implement gathering overall task capacity

For use when running/planning jobs

awx/main/migrations/0048_310_instance_capacity.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('main', '0047_v310_tower_state'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='instance',
+            name='capacity',
+            field=models.PositiveIntegerField(default=100, editable=False),
+        ),
+    ]