Do not track the .classpath generated by m2e

Different developers' versions of said file would interfere with each
other in a rather merge-conflict-prone way.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure that knime-ij-bundle/lib/ exists

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Let Maven copy the integration artifact into the bundle's lib/ directory

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Only copy the artifact automatically if the output directory exist already

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Move the Maven-specific git-ignores into the appropriate directory

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