added simple class to handle look and feel
improved gui to reflect native look and feel instead of jframe, added icon (placeholder)
Added invoice history table
Revert "Added invoice history table"

This reverts commit 989985f12b3e675adab4a208acd313db24fd4ace.
Revert "Revert "Added invoice history table""

This reverts commit 7c9480fa612a7f2ec927c636e3133f81e9674f07.
fix of bugs
Merge branch 'master' of https://github.com/truly-auto/SENG403
closes NEW ORDER tab once u click submit
Tab closing issue fixed. (closes the current tab)
created empty supermarket test class
fixing merge conflicts
fixed the table in NEW ORDER tab

- made the quantity column accept decimals only
- made the quantity column the only editable column
refactored parts of the database