Maybe convert into multimodule and validate workflows

[Artur-]

The current setup is non-standard in many ways and has the following issues:

• It can't be extended in any way
• It can't produce a demo war
• The Maven part is more complex than needed and hard to understand if you do understand Maven

Consider changing this into a multimodule project with one module for the addon and another for the test/demo (people tend to only create one UI and use it for both)

What needs testing is that this does not harm the development experience:

• Making a change in the add-on should not require mvn install or similar to test the demo in Eclipse
• Making a change in the add-on should not require mvn install or similar to test the demo in IDEA

Potentially the multi-module feature in Jetty 9.4.7 will help:

As of Jetty 9.4.7, when using jetty:run in a multi-module build, it is no longer necessary to build each of the modules that form dependencies of the webapp first. Thus, if your webapp depends on other modules in your project and they are present in the reactor at the same time, jetty will use their compiled classes rather than their jar files from your local maven repository.

[mvysny]

I've created a multi-module project here: https://github.com/mvysny/component-starter-flow