Change the manner in which active parts are filtered for BOM

- Prevented BOM from displaying for an inactive part
- Now manually filter the queryset in the form view

InvenTree/part/migrations/0013_auto_20190628_0951.py

@@ -0,0 +1,24 @@
+# Generated by Django 2.2.2 on 2019-06-27 23:51
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0012_auto_20190627_2144'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='bomitem',
+            name='part',
+            field=models.ForeignKey(help_text='Select parent part', limit_choices_to={'assembly': True}, on_delete=django.db.models.deletion.CASCADE, related_name='bom_items', to='part.Part'),
+        ),
+        migrations.AlterField(
+            model_name='bomitem',
+            name='sub_part',
+            field=models.ForeignKey(help_text='Select part to be used in BOM', limit_choices_to={'component': True}, on_delete=django.db.models.deletion.CASCADE, related_name='used_in', to='part.Part'),
+        ),
+    ]