Improve Presets management list page for Database activity

These testing instructions only check the features uncovered by behat. Setup Unzip the attached datapreset plugin (it's a clone of the imagegallery that only have been renamed) and copy the imagegallery2 folder into the mod/data/preset folder. Login as admin and install the datapreset plugin. Create a course. Add a database activity (with the default configuration). Create one field (it can be from any type and have any name). Click the "Save as preset" button that appears in the "Fields" tab and give a name to the preset. Testing instructions Access the database activity and go to the "Presets" tab. Check a brief description is displayed above the presets list, with an explanation of what presets are (something like "Choose a preset to use as a starting point."). Check presets table contains column headers (Name, Action). Check the Import button is displayed on the right, in the same row where the "Presets" title appears. Check the kebab action menu icon is not displayed for "Image gallery" and "Image gallery 2". Go to the "Fields" tab. Select "Use a preset" from the tertiary navigation. Check presets table contains column header Name, but Action is not displayed. Check there is no kebab action menu icon for any of the presets. Check that 'Use preset' button is disabled if no preset is selected