Editor permissions

The only option now is to adjust the capabilities that are required for users to access the store locator plugin screen through a filter.

If you add this to your functions.php, then users who can ‘edit_posts’ are allowed to add/edit stores. And editors are allowed to ‘edit_posts’ so they should have access, see http://codex.wordpress.org/Roles_and_Capabilities#Editor

add_filter( 'wpsl_capability', 'my_custom_capabilities' );

function my_custom_capabilities() {
    return 'edit_posts';
}