super().__init__() needed to be explicitly called for superclass instance variable to be initialized

- fix wrong signature for SeekEnv.__str__()

Fixes:
- missing parenthesis in ActionEnv
- ord() instead of int() in ChEnv
- VTTypes() needs to be initialized in InitParserBreakpoint, to get the correct gdb frame. Also keep references in TopLevelParse

Dependencies between script files are kind of a mess at the moment

- Add missing __str__() methods
- cast gdb.Value to int on creation

Also some boilerplate for GUI

Backend support for parser hierarchy widget