more helpful error message for corrupt collection package
prevent nesting things under filtered decks

This change keeps drag-and-drop behavior the same except for displaying
an error if an otherwise acceptable move would nest anything underneath
a filtered deck.
only display "added duplicate" message once

Even if there are several (duplicate) notes in the collection that
match, only send the message once to avoid making it look like multiple
dupes have been added.
add "export" button to deck menus
better message when Anki can't create a profile folder
dialog box size and position improvements

- keep track of size and position for a number of dialogs
- make sure addons dialog opens at an appropriate size for the system
  font size
- add optional argument to showText to restore geom on creation and save
  on reject (other buttons, if used, need to be programmed to save
  individually)
Merge branch 'geom_saverestore'