Add a class to read and write pom.xml files

This will come in real handy for the upcoming "bump" mojo to bump versions
in POMs. The job of mojo was previously performed by SciJava scripts'
bump-version-in-pom.sh script.

The most important part is that we modify the file contents as little as
possible, to avoid hiding the real changes between unsubstantial
formatting changes.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a class to hold groupId/artifactId/version triplets

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a unit test for the PomEditor

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
PomEditor: Add some API to extract information from the parsed POM

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add the "bump" mojo

Its purpose is to help SciJava projects maintain parent POMs, i.e. POMs
listing projects' current versions.

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