Apply multi-search on searching function for Item form and Purchase Invoice form
Fix login.py for wrong admin credential problem
Improve Item form and Purchase Invoice but still cannot delete; added Supplier form and also able to delete supplier
Added Customer form
Invoice able to delete
Revert "Invoice able to delete"

This reverts commit 1e19ce2edba78c2b3891f988f29f4108d1f7c9a1.