Fix deprecations

[txtsd]

I've replaced most of the deprecated methods with recommended ones.

I haven't touched any QTime methods since QElapsedTimer is monotonic and doesn't allow for conversion to human readable time. I've seen at least one instance of conversion to human readable time.
I also haven't touched QJSEngine because there is no alternative for the deprecated method.
There is another deprecation warning, but it didn't make sense to me so I left it alone. It's just a return nullptr but the output is this:

/home/txtsd/git/imgbrd-grabber/src/gui/src/ui/fixed-size-grid-layout.cpp: In member function ‘virtual Qt::Orientations FixedSizeGridLayout::expandingDirections() const’:
/home/txtsd/git/imgbrd-grabber/src/gui/src/ui/fixed-size-grid-layout.cpp:89:9: warning: ‘constexpr QFlags<T>::QFlags(QFlags<T>::Zero) [with Enum = Qt::Orientation; QFlags<T>::Zero = int QFlags<Qt::Orientation>::Private::*]’ is deprecated: Use default constructor instead [-Wdeprecated-declarations]
   89 |  return nullptr;
      |         ^~~~~~~
In file included from /usr/include/qt/QtCore/qglobal.h:1304,
                 from /usr/include/qt/QtGui/qtguiglobal.h:43,
                 from /usr/include/qt/QtWidgets/qtwidgetsglobal.h:43,
                 from /usr/include/qt/QtWidgets/qlayout.h:43,
                 from /usr/include/qt/QtWidgets/QLayout:1,
                 from /home/txtsd/git/imgbrd-grabber/src/gui/src/ui/fixed-size-grid-layout.h:4,
                 from /home/txtsd/git/imgbrd-grabber/src/gui/src/ui/fixed-size-grid-layout.cpp:1:
/usr/include/qt/QtCore/qflags.h:123:80: note: declared here
  123 |     QT_DEPRECATED_X("Use default constructor instead") Q_DECL_CONSTEXPR inline QFlags(Zero) noexcept : i(0) {}
      |       

Let me know if any behavior has changed.

[lgtm-com]

This pull request fixes 12 alerts when merging fb3ce09 into 6f4d5c1 - view on LGTM.com

fixed alerts:

• 7 for FIXME comment
• 3 for Resource not released in destructor
• 1 for Multiplication result converted to larger type
• 1 for Comparison result is always the same

[lgtm-com]

This pull request fixes 12 alerts when merging fb3ce09 into 6f4d5c1 - view on LGTM.com

fixed alerts:

• 7 for FIXME comment
• 3 for Resource not released in destructor
• 1 for Multiplication result converted to larger type
• 1 for Comparison result is always the same

[Bionus]

LGTM, thanks!

I'll see how much it prevents earlier systems from building it. Even though I don't mind dropping support for building on old systems.

[lgtm-com]

This pull request fixes 12 alerts when merging a764cf9 into 6f4d5c1 - view on LGTM.com

fixed alerts:

• 7 for FIXME comment
• 3 for Resource not released in destructor
• 1 for Multiplication result converted to larger type
• 1 for Comparison result is always the same