Added Indonesian translation
core: Allow NULL param in grl_date_time_from_iso_8601()
grl-inspect: Print slow keys

Show the slow keys list when inspecting a source.
core: Add clarification for max_page_size == 0

When using grl_paging_translate().
core: Adjust page_size to max_page_size

If page_size is NULL, then instead of computing the optimal page size, use
max_page_size as the optimal page_size.

This allows to use the function with those services that do not allow to
specify the page size.