Fix parent-child relationships for some Qt objects

[elfring]

:eyes: Some Qt objects are created without specifying a corresponding pointer for the parameter “parent”.

Examples:

• BackUp constructor https://github.com/CSMathematics/DataTex/blob/99fda6b887907f2e8e6b8f2425b09b0c7df1ccec/datatex/backup.cpp#L63-L65
• DataTables::LoadFields https://github.com/CSMathematics/DataTex/blob/a6eff0873df20c42df2ff33eb7f0554f53e625a0/datatex/datatables.cpp#L278-L283
• InfoPage constructor https://github.com/CSMathematics/DataTex/blob/a6eff0873df20c42df2ff33eb7f0554f53e625a0/datatex/basefolder.cpp#L75-L93
• LatexTextBrowser constructor https://github.com/CSMathematics/DataTex/blob/99fda6b887907f2e8e6b8f2425b09b0c7df1ccec/datatex/highlighter.cpp#L148-L152

:thought_balloon: I got the impression that such data would be required for safe management of parent-child relationships at more source code places.

[CSMathematics]

Indeed, there are many parts of code that need to be carefully considered.Τhanks for the remark .