Depend on Vala 0.16.1

We are using vfunc accessors for Widget.get_preferred_height/width which have
been added to this version.

https://bugzilla.gnome.org/show_bug.cgi?id=678072
add API to (un)highlight a widget during DnD

https://bugzilla.gnome.org/show_bug.cgi?id=678603
auto-scroll during DnD

https://bugzilla.gnome.org/show_bug.cgi?id=678782
Avoid warning when calling static method via instance
Convert EggListBox from vala to C

This is the initial pass, which is essentially a direct
conversion and needs more cleanup.
Bunch of formating changes
Clean up signal handling
Put ChildFlags stuff where used and simplify
Clean up the Block1Data thing
Reorder init/fini to start of file
clean up sort callback
Some formating cleanup
cleanup class_init
base -> container rename
base -> widget where appropriate
self -> list_box
Use priv locals
whitespace cleanups
Cleanup child visibility changes
Rename custom marshaller