CA Admin: New find content page, minor improvements and fixes

[chrieinv]

• Rename menu item in H5P menu from "Update libraries" to "Manage libraries"
• New menu item "Content info" for finding content by various ids
• Before deleting library also check if library is used by other libraries
• On Content details:
  • Add buttons for Preview and Export
  • List libraries
• Fix use of different date and time formats

ToDo: Add tests