* updated contents and format of pages
* updated <a> in 'index.html' with target="_blank"
* added 'archive' to INSTALLED_APPS
* updated ALLOWED_CONTENT_TYPES settings
* added app 'archive' to provides downloads
  o models: Archive, ArchiveCategory
  o views: ArchiveView based on TemplateView
  o template: archive.html
  o sidebar: sidebar.js, sidebar.css
* moved 'introduction.js' -> 'sidebar.js'
* moved 'introduction.css' -> 'sidebar.css'
* updated page introduction.html
* updated index.html and navbar.html
* included archive urls
* moved 'file_cleanup' function to extra.py
added INSTALL.txt