Document the use of Maven plugins for downloading and setting up browsers

[Legioth]

TestBench setup for each developer can be significantly simplified by using a Maven plugin that downloads phantomjs and/or e.g. Chrome Driver and installs them to a temporary location so that they are automatically available.

For phantomjs, com.github.klieber.phantomjs-maven-plugin can be used. For other browser drivers, com.lazerycode.selenium.driver-binary-downloader-maven-plugin seems to be the way to go.

This could be explained e.g. in https://vaadin.com/docs/-/part/testbench/environment/testbench-maven.html or as a new page under Best Practices.