This changes removes classes of the obsolete logging frame work and
all its references. It was not used anywhere, but included in several
headers.
Had to add header QDateTime in some places, which was not correctly
included and now missing.
refs #90
The new compare is implemented using "multimethods" described in the book Advanced C++ Programming Styles and Idioms by James Coplien.
First, the isA method is used to determine which of the values being compared is the most general. (For example, CLength is more general than CAltitude.)
Then the compareImpl method is called on the most general value, with the other value as an argument.
If there is not a direct inheritance relation between the two values (or they are the same class) then the comparison is invalid and a assert is triggered.
