Improve maven-ization of dcat files

[Aklakan]

The commands dcat mvnize metadata and dcat mvnize content currently always creates a dummy parent pom which includes:

• the deployment settings (based on a user provided template.pom.xml).
• references to all things to deploy as child modules

With the current approach, each deployment of metadata or content also attempts to deploy the dummy parent. This means that adding a revision requires adding a new parent version.

Instead, there should be only a single 'bom'-like parent with the deployment settings that a user deploys infrequently when settings need to change. A specific version of this bom is then used as the parent across several dataset/metadata deployments.

The advantage of the dummy parent is, that all child modules can be deployed using a single mvn deploy command.

• Clarify: Is it possible to have a dummy project which references several child modules, whereas the child modules themselves have the bom as their parent? (i.e. the children do not link back to the dummy parent)

pom.xml # refererences child1 and child2 module but children don't reference back
child1/pom # references global bom
child2/pom # references global bom

[Aklakan]

Looks like it is possible to have a 'convenience' parent in order to deploy a batch of child modules (where each child may point to a different parent) - with a dummy pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>dummy</groupId>
  <artifactId>dummy</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <modules>
    <module>my-dataset1</module>
    <module>my-dataset2</module>
  </modules>
  <build>
    <plugins>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>3.1.1</version>
          <configuration>
		<skip>true</skip>
	  </configuration>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>3.1.1</version>
          <configuration>
		<skip>true</skip>
	  </configuration>
        </plugin>
    </plugins>
  </build>
</project>

The only caveat so far is, that children need to have an empty relativePath to disable resolution against the parent folder - and thus to get rid of a warning:

<!-- In my-dataset1 -->
<parent>
  <groupId>org.aksw.dcat-suite</groupId>
  <artifactId>aksw-deployment-bom</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <relativePath></relativePath>
</parent>