add default arguments functions
add functions for controlling look of login page
All - Removed contextual actions, filters and functions (out of scope).

inc/conditionals.php - fixed issue with $function_name() passed as a parameter to slimline_conditional_safe() instead of $function_name

inc/post-template.php - moved slimline_body_attributes, slimline_comment_attributes and slimline_post_attributes filters to slimline_{$context}_attributes, added slimline_get_{$context}_attributes filter.