adding surcharges and bills.
Merge branch 'dirty' of https://github.com/shagun30/LibreHatti into shagun30-dirty

Conflicts:
	src/librehatti/catalog/models.py
	src/librehatti/print/views.py
Merge branch 'shagun30-dirty' into dirty
Merge branch 'dirty' of https://github.com/piyushparkash/LibreHatti into dirty