Optimize Documentation in Extension Portal and Description in github

[volkerstorm]

Description

Some additional entries in the documentation.

Motivation

Some additional entries in the documentation could help to get faster in test and operation with this very interesting and potentially very useful plugin.

Proposed Solution (optional)

• Add the direct link to the compiled jar-File in the extension portal: https://github.com/SchweizerischeBundesbahnen/ch.sbb.polarion.extension.cucumber/releases
• Add the installation manual to the extension portal and mention that the directory /polarion/data/workspace/.config has absolutely to be deleted before restarting Polarion
• give some more details how to configure Maven builds on the Polarion server