Various improvements

fixed:
#341078: Warning when no vocabulary is available
#371520: Empty rows cluttering the UI
#401846: Call to undefined: taxonomy_get_vocabularies()
#420598: Pager appends unnecessary form data to URL
#426494: Pass input text through check_plain before displaying
#441478: Support for deleting menu item translations

code for admin pages separated to different file, to reduce the memory usage
code rewritten to use the FormAPI (removed $_POST and $_REQUEST)
theme functions created