jump to newly created sections, fixes #251
display exercise titles, fixes #256
fix element boundaries in navigation, fixes #258

When a section's title is really long, the wrapping anchor element's
height in the section navigation is expanded to fit the title. Then,
the navigation's list elements overlaps the section's blocks.
change button order, fixes #257

The order of the save and cancel button when editing chapters and
subchapters was changed in 3725e1b5de19375faeba3af60d7156eafcc619a4.
For consistency, this commit changes the order of the buttons
accordingly in the section edit view.