Improved document metadata viewers: comments, attachments, history, information, code

Improve the various metadata viewers by:

• using better localization keys and messages, and translating a few tokens left untranslated
• remove commented code
• improve the codestyle and velocity parsing performance
• display attachment size with one decimal precision, instead of integer size (1.7Mb instead 1Mb)
• remove an extra space between the attachment size and the closing bracket: (123 bytes ) => (123 bytes)
• added js confirmation when deleting a range of versions from the history, and removed this button when there's only one version
• added link back to the document view mode, instead of a simple <em>
• made the information header consistent with the other ones (was h2 instead of h1)
• removed unneeded empty <label> elements from the information tab
• added translation information