Issue 6818 - Added ability to declaratively translate attribute values

This MR for #114 (closed) contains the following changes:

• Added support for:
  • [data-i18n]
  • [data-i18n-alt]
  • [data-i18n-placeholder]
  • [data-i18n-title]
  • [data-i18n-value]
• Marked [class^="i18n_"] approach as deprecated.
• Renamed a few variables in loadI18nStrings() function and removed redundant comment.
• Use new syntax in first-run.html to show impact on existing code.