Bugfix for Antora preview for file names with blanks

• Fix parsing of nodes enumerations inside of blocks
• No longer look outside the project folder for context information like .asciidoctorconfig files or Antora component descriptors (#1279)
• Support hard unset attribute for Antora component descriptors and playbooks (#1278)
• Avoid outdated path information for the preview after moving a file (#1276)
• Remove special handling for file names on Windows with blanks (#1276)