externalize-project: do not require pom-fiji-plugins as parent

The last remaining two projects in src-plugins/ do not have that parent...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Jama is an external project now

As of 3a3545f(Add a .gitignore file), Jama lives in

	https://github.com/fiji/Jama

It is not linked in external/pom.xml because it was not built by default
anyway.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ignore if Jama is cloned into external/

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater_Fix is an external project now

As of b00c843(Add a .gitignore file), Updater_Fix lives in

	https://github.com/fiji/Updater_Fix

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ignore if Updater_Fix is cloned into external/

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

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Do not drag Updater_Fix in by default

That artifact was never intended to be a default part of a Fiji setup; it was only needed due to a bug in the Fiji Updater, now long fixed and forgotten.

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