- F2 is now an accelerator for rename

- F2 is now an accelerator for rename
- panel switching via TAB doesn't use IsDialogMessage anymore
- focus is correctly set after main window activation (Alt+TAB etc),
  removed some focus-related bugs
- pressing ENTER or double-clicking a value edits it
- setting a value to an empty string is now allowed
- adding a new value starts rename automatically
- renaming a value doesn't move the cursor
- removed some unnecessary code (NM_RCLICK in ListView etc)
- right-click on tree view displays "New..." menu
- default values are treated like in Windows RegEdit (displayed even
  when they aren't physically present, can't be renamed or deleted)
- Polish translation had some weird characters added before Polish
  letters