Improved part logic

- Added field 'buildable' - can this part be made from other parts?
- Added @propery 'supplier_count'
- Improved part detail page with new features

InvenTree/part/migrations/0018_part_buildable.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11 on 2018-04-16 12:08
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0017_part_purchaseable'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='part',
+            name='buildable',
+            field=models.BooleanField(default=False),
+        ),
+    ]