Provide ZAP wrapper application argument to disable headless mode

[de-jcup]

Situation

Currently the wrapper application uses always the headless variants of the webdriver browsers.

For development / testing it is sometimes necessary to see whats going on (e.g. developing custom groovy login scripts).
To enable this we must currently change code temporary - which is cumbersome and potentially error prone.

Wanted

As a developer I want to start the ZAP wrapper application in non-headless mode as well.
In non-headless mode, the browser used by ZAP shall be "non-headless" and also the selenium parts of custom login scripts shall be "non-headless" in this case.

Solution

• introduce command line parameter --headless which default is true
• switch used browser (name) by Zap by this parameter
• switch webderiver setup for script by this parameter as well