give a sane minimum size to the dexter window

[Robert Roth]

When resizing dexter to its minimum size, the toolbar gets truncated, and the last items are put into a dropdown, and the import buttons are cropped. A minimum width should be set for the toolbar to be displayed fully everytime, and a minimum height should be set to be able to display the two buttons from the welcome screen. See the screenshot for the current look at minimum size.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: dexter 0.18-1~nnpostler1
ProcVersionSignature: Ubuntu 2.6.38-7.36-generic-pae 2.6.38
Uname: Linux 2.6.38-7-generic-pae i686
Architecture: i386
CrashDB: dexter
Date: Mon Mar 21 23:54:06 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha i386 (20110202)
ProcEnviron:
 LANGUAGE=en_US:en
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: dexter
ThirdParty: True
UpgradeStatus: Upgraded to natty on 2011-03-09 (12 days ago)