implemented exporting of favorites list as xml file (.nkpd)
fixed bug where a canceled export dialog would still try to run code
implemented "import from file" option for drop stack. Also changed a the date attrs in ToolItem to use getter/setter logic to make it easier to convert between time objects and strings
tidied up login page after failed log in
implemented marking of tools to indicate whether the online version is newer than it's local sibling - for debugging this currently marks all local tools as needing an update