Fix a flock of little things in the hypview GUI:
. Improve control panel layout by removing spacers and using Border spacing instead. . Start to make resizing work by setting Expand options in the GUI. . Change the LabelsMode widget from a wxComboBox to a wxChoice. . Disallow non-numeric chars and handle Enter in the "Node/Link depth" spinboxes. . Handle Enter in the Open dialog text fields; complain politely about empty text. . Disable show/hide buttons when there are no links in or out, respectively.