remove pragma:no-cache header. closes #1201

The pragma header is only defined for requests not for responses. The
Cache-Control header should be used in responses.

Add a 'returnonly' option to all xhtml link types

translation update

fixed a few links and html errors in language files

fixed some wrong quotation marks in language files

fixed occurrences of html named entities in translation files to be xhtml-compatible

removed English translation strings from non-English translation files

fixed lots of missing format strings in language files

refactored tpl_actiondropdown() to avoid duplication

changed all input type=submit buttons to button type=submit button for better stylability

translation update

translation update

translation update

translation update

undefined var

Use a DateTime object in the IXR_Date

phpdocs, reformatting

translation update

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translation update

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translation update