Do not ruin great debug messages from YAML parser

Also fix "next_result" command (F4) not working. Don't ask me why this is
required but it's also in exec.py.
Slightly revise some older source files
Revise YAML syntax def completions

- Don't always inhibit default completions when no nodes where found
- Fix base suffix not appearing
- Do not show base suffix when it is already the last token
- Additionally, remove duplicated code for creating a new syntax def
Update main menu to YAML syntax (forgot about that)
Rearrange YAML Syntax def: Better single-line map detection

This essentially means that it also handles 2 and 3 single-line maps and even
when in a mapping value (e.g. repo key) instead of "being more accurate".
Rearrange YAML Syntax def: Add feature to add newlines at certain positions