Improve navigation between preset action assignment and and preset list

On themes where breadcrumbs are not displayed, navigating the imagecache UI can be troublesome.

It would be useful if the "save preset" action on the imagecache_ui_preset_form returned the user to admin/build/imagecache.

Alternatively, it would be nice to have the "add a new preset" button (or tab) on an existing preset form, or provide some other easy way to navigate back to the preset list, and on to the next preset.