topic-branches.sh: let the environment variable REMOTE override

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

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add ij-app as a dependency of fiji-compat

This is needed for the upcoming Help>Switch to Modern Mode command.

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