Merge pull request #9 from williambernardet/master

Fix proposal for JENKINS-18345
[maven-release-plugin] prepare release ws-cleanup-0.15
[maven-release-plugin] prepare for next development iteration
[JENKINS-18446]: Check optional env variable if ws should be cleaned up.

Signed-off-by: Florin Hillebrand <florin.hillebrand@streamunlimited.com>
Rename help file to be loaded
Keep backward compatibility and for boolean values use boolean
Fix SNAPSHOT version
[maven-release-plugin] prepare release ws-cleanup-0.16
[maven-release-plugin] prepare for next development iteration
Show matrix related options only for matrix jobs
Fix German translation encoding (based on PR #11)
Allow external tool to be used for deletion (such as unlocker)

 - If a node has delete_command environment variable, it will be used
 	instead of the default functionality.

The format of the command is:
"path/to/executable" [options] %s

Unlocker, for example:
"C:\Program Files\Unlocker\unlocker.exe" %s /D /S
Deletion tool can be configured in the delete workspace settings.

Allows for expansion of variables so per-node configuration is still
available.
[maven-release-plugin] prepare release ws-cleanup-0.17
[maven-release-plugin] prepare for next development iteration
[FIXED JENKINS-19574] Restore backward compatibility in prebuild cleanup
[maven-release-plugin] prepare release ws-cleanup-0.18
[maven-release-plugin] prepare for next development iteration
Use list instead of string for ProcessBuilder
Merge pull request #13 from jacobgardner/master

Use list instead of string for ProcessBuilder For External Deletion Tools