semi-fix tabbing of elements

This fixes the issue where tab wasn't setting its cursor
focus on the buttons. One issue remains is during a 'shift tab'
while the current focus is on 'cancel' it jumps back to
the last input item rather than shifting over to the 'ok'
button.

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
split out boxadapter from inherited widget

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Merge pull request #226 from Ubuntu-Solutions-Engineering/patch-fix-tabber

Patch fix tabber