Don't redirect to /camunda if webapps are not enabled

[tobiasschaefer]

Even if the webapps are not enabled the redirect to /camunda is enabled by default. The redirect only makes sense if the webapps are enabled.

• We probably just need to add a "requires" for property camunda.bpm.webapps.enabled=true
• We probably need another simple test for this scenario.
• Please also add a short javadoc to class "RedirectToWebappsController" what the class is about.