Make 'tiny' image size configurable

[jazzsequence]

probably on the options page

see https://wordpress.org/support/topic/request-tiny-size-used-in-widget-should-be-configurable?replies=2#post-8208209

[jazzsequence]

should add a filter to handle this, so an image size can be added via code or in the back-end and either will hook to the filter that returns the default image size.