Make filter editor available in UI

[Anders Melander]

Currently the grid can be filtered via the filter buttons in the column headers.

This feature isnt very obvious to the user and doesn't surface the full range of the grid’s filtering capabilities.

The task for this issue is:

• Make the filter editor accessible.
• Add support for both predefined and custom filter sets.

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[Anders Melander]

Right now the filter editor is available when a filter has been defined (via the column headers). This will have to do for now.