Some mangling, refactoring and fix PDF download

[mondeja]

Contributes to #286

• Fix PDFs not being downloaded using the download mode button.
• Remove xmlns from inline SVGs (see this question on StackOverflow)
• Refactor some code.
• Remove duplication of download link href and preview src.
• Merge order-color and order-alpha attributes into one o attribute separating the values by a - character.

Size before

  index.html (2.17 MiB)
  es/index.html (2.2 MiB)
  fr/index.html (2.19 MiB)
  it/index.html (2.19 MiB)
  pt/index.html (2.18 MiB)
  zh-CN/index.html (2.18 MiB)
  zh-TW/index.html (2.17 MiB)
  zh-HK/index.html (2.17 MiB)
  ja-JP/index.html (2.2 MiB)

Size after

  index.html (1.96 MiB)
  es/index.html (1.99 MiB)
  fr/index.html (1.97 MiB)
  it/index.html (1.98 MiB)
  pt/index.html (1.97 MiB)
  zh-CN/index.html (1.97 MiB)
  zh-TW/index.html (1.96 MiB)
  zh-HK/index.html (1.96 MiB)
  ja-JP/index.html (1.99 MiB)