Bug Submitter: use the same dialog instance again after failure

This fixes Bug #816 in Fiji's bugzilla:
http://fiji.sc/bugzilla/show_bug.cgi?id=816

I had minor troubles when building with Maven: imagej-updater-0.3.9.jar gets deleted and replaced by an earlier version (0.2.0, or 0.3.6 if I removed the version tag in pom.xml). When I removed the imagej-updater dependency completely (thinking that it's implied by pom-fiji), I got compile errors, so I left it in, but had to put back the newest imagej-updater.jar in Fiji.app/jars in order to be able to start Fiji.