add a configuration option for the "move the cursor to the end"

So the way I write mail is often, I hit "reply", then I actually read through the mail from the top down in terms of the quoted text, and add my comments inline.  So I like to still start at the top.

The one issue I'm having with the patch here is that the "defaults" thing isn't working on Maverick.  If I set `defaults write uk.me.cdw.MailWrap PlaceCursorAtEnd -bool false`, that puts the value in there, but that does not seem to be what `bundle.objectForInfoDictionaryKey_('PlaceCursorAtEnd')` is reading; all of those calls continue to read from what was set up in install.py.  Any tips on how this should work appreciated.