Implemented Array:containsOnlyValue.
Restored implementation of ArrayOperations::memoryCompare on host.

Implemented a method Array::checkValue which returns true only if there is an element with given value in the array.

I don't understand how it could work on the small grids...

The Host class was combining too many things...

It actually does not affect anything...

Why do problems have this method anyway? It was obviously never used...

When type traits for the "double-float" or "double-double" types are
needed, they should be added as specializations of the
std::numeric_limits template in some of the TNL header files.

There were 2 problems:

- it does not belong into a numerical library
- the approach with hardcoded escape codes is not portable even on Linux

There are separate libraries which solve both of these issues much more
nicely, they should be used instead.

And of course our implementation is faster ;-)

It cannot work because indices are not initialized to -1 anymore. The
checks in the MeshBuilder class should be enough.

This way GCC does not complain that they are not used in some
compilation units.

It should not be called "base" because inheritance does not work for the
constexpr methods.

It is checked in the ConfigValidator.