When restarting an updated Updater, wait until it finishes

This allows the Fiji_Updater.jar to catch exceptions and fall back
to the remote updater.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Do not let a missing uploader service stop the updater from running

The problem occurs when updating the updater: all of a sudden,
formerly existing .jar files cannot be opened any longer, and that
means that the uploader service might not be found.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'update-the-updater-fixes'

The problem this branch tries to solve is to make updating the updater
less tedious.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>