[JENKINS-12199] Fixed bug where job configuration shows a displayname even though the job doesn't have a display name

[JENKINS-11762] Fix displayname issues when renaming or cloning a job. We now clear the display name when cloning or renaming a job.

- I feel uncomfortable with a string field used as an enum.
- I feel uncomfortable with parameters that have some restrictions about
  the way they can be combined.

My change is bit more verbose but it uses less Jelly and I think it's
more in line with the architecture.

- 3 options : run as Local System, Administrator or custom account
- Memory options
- Disconnect the slaves stops correctly and deletes the service
- Reconnecting the slave updates the jenkins-slave.xml configuration

- Loop only on tags between block-start and block-end
- Clearer and shorter code

1) Installer checks Java is installed before proceeding.
   It also tells how to get Java installed.

2) Installer opens http://localhost:8080 when installation is finished.

[FIXED JENKINS-12119] rolling back a portion of 46998ba0446834de0c725c32b328ace7ce844f6a as this is binary incompatible change

The ZipArchiver was visit()'d with a relative path that uses the system's path
separator, but zip archives require a forward slash for platform compatibility.
This fix replaces the platform-dependent File.separatorChar with a forward
slash.

user name