Move JNI Example files in preparation for Mavenization

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a pom.xml file for the JNI_Example project

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ignore Maven products in the JNI_Example

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix compiler warnings identified in JNI_Example.c

These warnings are only now apparent due to NAR's default options.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
JNI_Example: use the JNI library name generated by NAR to load it

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Re-add FFMPEG plugin file that was removed by mistake

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