new module: monthly report
new module: custom range report
new module: credit

- list credit
- list credit payment
- pay credit
new module: crud unit
new module: crud customer and supplier
refactoring monthly report view

- minor bug fix
change amount field from integer to decimal
fix bugs
add module: customer-detail
added debit table
finished adding debit module

added feature:
- right click to edit product's code and name on list-stock
- add-variant is now replaced with full featured add-stock (for more
option)
massive changes on database structure

customer and supplier table are now bended into one second_party table
added feature

- debit and credit report
- daily transaction chart on custom range report
add sales cashier report
Merge pull request #5 from nicklaros/development

Push to GA release cycle