fix: Sider, Linter and Server Side Test

- Fix Server side PR test
- linter: re-arrange imports
- sider: avoid single line multi statement
- Code cleanup: Improve code readability and avoid horizontal scroll in test_purchase_receipt
- Removed unused variables in test_purchase_receipt

(cherry picked from commit 293f6cbafd)

# Conflicts:
#	erpnext/stock/doctype/purchase_receipt/test_purchase_receipt.py

erpnext/controllers/buying_controller.py

@@ -4,7 +4,7 @@
 from __future__ import unicode_literals
 
 import frappe
-from frappe import _, msgprint, ValidationError
+from frappe import ValidationError, _, msgprint
 from frappe.contacts.doctype.address.address import get_address_display
 from frappe.utils import cint, cstr, flt, getdate
 
@@ -17,7 +17,9 @@ from erpnext.controllers.subcontracting import Subcontracting
 from erpnext.stock.get_item_details import get_conversion_factor
 from erpnext.stock.utils import get_incoming_rate
 
-class QtyMismatchError(ValidationError): pass
+
+class QtyMismatchError(ValidationError):
+	pass
 
 class BuyingController(StockController, Subcontracting):