Use megabytes instead of gigabytes for size calculations internally. Change variable types to "int64_t" for megabyte calc.

Add function "getSizeTextFromMegabytes" for generating size strings where it was repeated code.
Optimize code to do less reading of reusable locale strings and read "logicalBlockSize" before reading other size parameters.

include/mainwindow.h

@@ -95,4 +95,11 @@ private:
     void addSmartAttributesTable(const QJsonArray &attributes);
     void transformWindow();
     void mousePressEvent(QMouseEvent*);
+
+private:
+    QString mbSymbol;
+    QString gbSymbol;
+    QString tbSymbol;
+    QString pbSymbol;
+    QString getMbToPrettyString(const int64_t &sizeInMbI64, const int &precisionInt, const bool &useGbBool);
 };