Provide download link to export BOM file

- Helper function for generating temporary file (in memory) for exporting

InvenTree/InvenTree/helpers.py

@@ -0,0 +1,32 @@
+import io
+import os
+from wsgiref.util import FileWrapper
+from django.http import StreamingHttpResponse, HttpResponse
+
+
+def WrapWithQuotes(text):
+    # TODO - Make this better
+    if not text.startswith('"'):
+        text = '"' + text
+
+    if not text.endswith('"'):
+        text = text + '"'
+
+    return text
+
+
+def DownloadFile(data, filename, content_type='application/text'):
+    """
+    Create a dynamic file for the user to download.
+    @param data is the raw file data
+    """
+
+    filename = WrapWithQuotes(filename)
+
+    wrapper = FileWrapper(io.StringIO(data))
+
+    response = StreamingHttpResponse(wrapper, content_type=content_type)
+    response['Content-Length'] = len(data)
+    response['Content-Disposition'] = 'attachment; filename={f}'.format(f=filename)
+
+    return response