Build WebVOWL and OWL2VOWL from source in Docker

[htafer]

Replace external WAR download with multi-stage Docker build that:

• Builds OWL2VOWL converter from GitHub source using Maven
• Builds WebVOWL frontend from local source using Node.js
• Deploys both to single Tomcat instance with merged context

This fixes the issue where the downloaded WAR file was corrupted or unavailable, and enables ontology conversion functionality by including the OWL2VOWL backend service alongside the WebVOWL frontend.

The OWL2VOWL servlets (serverTimeStamp, convert) are now accessible at the same context path as WebVOWL, allowing the conversion service to work correctly.

Works both for docker and podman

Changes:

• Use multi-stage build with maven:3-openjdk-8-slim for OWL2VOWL
• Use node:12-alpine for WebVOWL build
• Use tomcat:9-jdk8-openjdk-slim runtime (JDK needed for jar command)
• Extract OWL2VOWL WAR and overlay WebVOWL static files in ROOT context