#92 Fixed version qualifiers and other version improvements

• Use single fixed version qualifier for all plugins/features/etc.
  • Defaults to 'dev'.
  • Replaced in Jenkinsfile for Jenkins builds.
  • Include -M1, -RC1 etc postfix in qualifier for non-final releases.
• Renamed releaseVersion to escet.version.enduser.
• Replace qualifiedVersion by end user version.
  • Gives simpler, more readable names for the download archive file names.
  • Gives simpler, more readable names in generated documentation.
• Customized website download archive filenames to be more readable.

Closes #92 (closed)