tip-view: avoid the viewport

The TextView has native scrolling. This simplifies the code a bit and improves resizing.
dialogs: fix resizing

In contrast to gkt+2 in gtk+3 contain_add is not setting expand. Switch to
box_pack_start to ensure content enlarges when the window enlarges.

Fixes #41.
registry: rename api from _find_ to _get_

This is in sync with the api in device, that has get_by_name().