Added file removal by pressing delete
Added shell execution for addon's files
Fix severe bug resulting in stack overflow
Exception rethrow fixes to preserve stacktrace
Merged UpdateMetadata functionality into Main form
Show the dialog for loading other addon while one is unsaved if it's truly unsaved
Removed duplicate catches for addon file add restrictions
Made the interface more user-friendly with easier error messages

Also changed the way the long error filelists are handled. They usually
caused too big and off-screen MessageBoxes. New method writes the list
into a temporary file and opens it in notepad.
Updated README and changed version number to 1.1