upload-plugin-from-maven: delete the artifact before installing

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
upload-plugin-from-maven: force overwriting dependencies

This is necessary e.g. for SNAPSHOT-versioned dependencies.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
upload-plugin-from-maven: use imagej-maven-plugin version 0.5.1

This has a bug fix: the top-level artifact is now installed, even if
its scope is not set, technically.

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