Move BomItem into the Part app

- Does not make sense to keep these separate
- Removed bom app entirely

InvenTree/part/serializers.py

@@ -1,6 +1,16 @@
 from rest_framework import serializers
 
 from .models import Part, PartCategory
+from .models import BomItem
+
+class BomItemSerializer(serializers.ModelSerializer):
+
+    class Meta:
+        model = BomItem
+        fields = ('url',
+                  'part',
+                  'sub_part',
+                  'quantity')
 
 """
 class PartParameterSerializer(serializers.HyperlinkedModelSerializer):