Added Maven Build

[tisoft]

Current status:

• Maven compiles all existing projects
• All runtime dependencies are correctly handled
• All (including transitive) dependencies are pinned to the versions used by ant
• Find released maven artifacts for dependencies currently handled as system
• Build artifacts actually work
• Tests pass
• The same release artifacts are created, as Ant does
• Artifacts are signed
• Artifacts are deployed on Maven Central

Not in scope for this PR, since we might want to have both build systems work in parallel for some time

• Remove ant build files and library Jar files from repo
• Reorganize project structure to match Maven (e.g. src/main/java)