simplified shortcut import

No longer tries to match games against existing profile entries. Deletes
all old shortcut games an imports new ones.

Also no longer imports shortcuts when the gamelist is downloaded, only
on config import.
additional shortcut modifications

Replaced ignore externals profile setting with include shortcuts setting
both in the dialog and the config file. Is true by default.
Removed leftover code related to importing shortcuts on download.
All profile XML element names now stored as class constants.
Fixes to Include Shortcuts option

No longer displays shortcuts in the game list if the option is disabled
No longer saves the shortcuts to the profile file if the option is
disabled