Attributes: Noticed log_message() being called with uppercase letters in the level which causes errors in the system; Customers: improved the layout of the stats page in the information dialog issue 3892; Items: got csv import working issue 3896 and bulk edits working - barcode generation does not work yet.
- Replaced TRUE/FALSE constants with true/false keywords
- Replaced NULL constant with null keyword
- Replaced `<?php echo` in views with shortened `<?=`
- Added missing variable declaration
- Added missing function return type in declaration
- replaced `== true`, `== false`, `=== true` and `=== false` in if statements with simplified forms
