add new 'access send to friend' and 'access PDF version' permissions to any role which has 'access print'

Fix for #364535: add some warnings about incompatibility of custom strings and the localization mechanism
Add explanation of the relation between the type- and node-specific print settings
Updated all translations (Dutch 100% thanks to joostvdl)

Improve variable cleanup at uninstall

Fix #247578: Print URLs by content type
Fix #298063: Most printed, emailed and PDFd blocks