Responsive Image attributes and other fixes

Changes for Theme Developers

• You can now change the query parameters that are used when getting a post’s terms through $post->terms(). #1802
• New attributes for responsive images post.thumbnail.srcset and post.thumbnail.sizes #1819 (thanks @maxxwv)

Fixes and improvements

• Using WordPress's wp_check_filetype_and_ext for the mime_type mess #1843 (thanks @gchtr)
• Fixed how some previewed data (when looking at an unsaved post from the admin) is handled so that parenting relationships match what happens when published #1752
• Timber\Menu now respects modifications sent through WP's wp_nav_menu_objects filter #1814 (thanks @pascalknecht)