magic pack template now uses 'pack type' instead of 'pack item'

don't allow a new pack to be 'removed'

custom pack types can now be removed again.

use set_help_text instead of the previous thing in SetWindow.

   typing1 Ctrl+Z Ctrl+Y typing2 Ctrl+Z
removes just typing2, not both.

There is no UI for using these custom types yet.

- added DoGetBestSize to PackTotalsPanel, so the text always fits

- The tag_contents script function now works as advertised:
     - uses 'input' script variable instead of 'contents'
     - keeps the full old tag, not the one from 'tag'
     - no template code in svn breaks.

added check_tagged function that verifies that a tagged string is correct, this helps with debugging.

fixed bug in keyword parsing: seperator_after contained the whole string, causing it to be duplicated