Switch to node-based Saxon, eliminate Ant and Java from the stack

[rolfkleef]

We started working with Ant to benefit from build tool features, such as only processing a file when it is newer than the targeted output, and declarative specification of steps.

Together with Saxon-HE and BaseX, this resulted in a Java-oriented stack.

In the "pure S2I" version, the transformation steps are more linear and straightforward, and since we're running each conversion "once per container", much of the benefit of a tool like Ant is no longer used.

In the meantime, there is a nodejs-based version of Saxon. As we're trying to eliminate (bulky) components from the convertor, we can test conversion performance of both Saxon versions, and perhaps consolidate on a pure-node/javascript stack.