Previously relied on the presence of a last column which wasn't filterable,
commonly a GridFieldEditButton. If this wasn't present, the filter buttons
were never added, leading to the GridField JS reload request being sent
without the required button form action, so GridFieldFilterHeader->handleAction()
was never called.
The entire framework repo (with the exception of system-generated files) has been amended to respect the 120c line-length limit. This is in preparation for the enforcement of this rule with PHP_CodeSniffer.
1. Modified gridfield to use default colours
2. Added ability to show and hide the filter
3. Design changes to icons used
4. Gridfield template fixes: Took out broken mark-up from templates
(spans were being inserted inside spans), and adjusted styles. Added
extra class to template
5. Added "filter by ..." placeholder text to input fields